Friday, September 9, 2011

Italian Small Submarines, Updated

(updating ongoing work in progress)
Since before the Second World War, Italy has been a prolific designer and producer of small submarines. The CA and CB-class midget submarines and their operational histories are already well-known, but those produced post-WWII are much less known, poorly documented and the subjects of confusion and misinformation. Fincantieri, Maritalia and Cos.Mo.S. are all known to have produced viable small submarine designs, however only Cos.Mo.S. is known to have definitely produced actual small submarines, albeit all for export.

This file is intended to serve as a repository for actual and projected post-World War 2 Italian small submarines designs. As always, comments and additional information are welcomed.

Cos.Mo.S. SpA, Livorno
Over the course of its 48-year history from 1955 to 2003, Cos.Mo.S. is believed to have produced a total of 24 midget submarines. Of these, 20 were delivered to five export customers, three were sold to Iraq but never delivered, and one remained at the Cos.Mo.S. factory as a demonstrator and developmental testbed.

Because of Cos.Mo.S' very secretive business practices, it may never be possible to completely ascertain all their boats' deliveries, but the most likely breakdown of their actual midget submarine deliveries is as follows (Provisional):
Type                          Date               Quantity                  Customer
SX-404                       1969                2                                  Taiwan
SX-404/B                  1972                 6                                  Pakistan
SX-506                       1973                 2                                  Colombia
SX-506                       198?                 2                                  Republic of Korea (i.e. South)
SX-756/K                   198?                 5                                  Republic of Korea
SX-756/W                 1985                  3                                  Pakistan
SX-756/W                 1989                  2                                  Iraq (never delivered)
SX-756/S                   1989                 1                                  Iraq (never delivered)
MG-120/ER              unknown          1                                  Demo boat retained at factory

Cos.Mo.S' midget submarine designs were an ongoing evolution and expansion of essentially the same design over the course of 45 years from the mid-1960s to the company's demise in 2003. Its midget submarine designs were originally designed to transport naval special warfare forces and swimmer delivery vehicles into a target area, and as such lacked an organic attack capability.  The company frequently marketed the same design under different designations to multiple potential clients. The reason for this practice is not known; possibly it was intended to reduce the possibility of clients becoming aware of each others' capabilities and Cos.Mo.S' relationship with them, or possibly it was simply to create the impression that Cos.Mo.S produced and sold more units than was actually the case.


SX-404 was Cos.Mo.S’ first known venture into midget submarine design and production. This was a 40-ton boat intended to transport naval SOF operators into hostile waters over distances greater than those that could be achieved by the company’s Chariot swimmer delivery vehicles (SDVs). All Cos.Mo.S’ midget submarines were designed with the capability of carrying two of the company’s CE2F-series SDVs.

Cos.Mo.S built two subvariants of this design, the SX-404, two examples of which were delivered to Taiwan, and the SX-404/B, six of which were delivered to Pakistan. The two subtypes are easily distinguished from each other by the presence or absence of a large horseshoe step on the sail. Pakistan’s SX-404/Bs have this step, Taiwan’s do not.

Displacement:          40 tons

Length:                     59.1 feet
Width:                       6.5 feet
Draft:                         8.4 to 10.4 feet
Surface Speed:         10kts (designed), actual 4kts
Submerged:              7.2 kts
Max depth:               131.2 feet
Range:                       1235 nautical miles
Crew                          4 Officers, 2 NCOs, 6 passengers
Payload:                    2 SDVs (CE2F Chariots)

Taiwan was Cos.Mo.S’ first midget submarine customer, taking delivery of two in 1969. As originally delivered, Taiwan’s boats had rounded bows, which were later modified to the more common ship-type bow seen on most other of Cos.Mo.S’ boats.  The two boats, S-1 and S-2 served until 1973.  Both boats are preserved and are on public display at the Taiwan Naval Academy.

In the late 1960s, Pakistan ordered six SX-404s to a slightly modified design. The Pakistani Navy deployed its six boats against the Indian Navy during the 1971 war. One of them, reportedly fitted with external torpedo tubes fired on an Indian naval frigate, INS Kukri, but the torpedo remained stuck in its external launcher. Of the six, one was lost with all hands as a result of an accident on December 27, 1976. Following removal from service, four were scrapped and one was placed ashore as an exhibit in the Pakistan Maritime Museum in Karachi.


S20 ARC Intrepido
S21 ARC Indomable
1972 - 07 August: Arrival in Colombia
1973 - 17 April Intrepido commissioned
1973 - 03 July Indomable commissioned
1980 - both modernized, lengthend 6ft to accommodate air conditioning unit
1995 - batteries replaced; auxiliary systems updated to incorporate automatic load control
1998 - 1st participation in annual UNITAS exercises
2003 - steel plating on outer hull casings replaced with anticorrosive steel at COTECMAR
Missions: shallow-water operations, commando operations, tactical amphibious reconnaissance, underwater demolition, attacks on port facilities, offshore installations, anchored or moored targets, beach surveys and intelligence missions.
1x Cummins diesel-electric, 300hp
1x 75hp engine generator
Battery: 24V 1100 Amp
1x screw
Surface:              75 tons
Submerged:       90 tons
Endurance:        20 days
Dimensions (2010):
Length:               23 meters
Beam:                 2.2 meters
Height:               4 meters
8x explosive charges from 50kg to 2050kg, including the charges onboard chariots.
Mines: 6x Mk-21; 8x Mk-50.
Other Equipment:
2x CE2F/X-60 Chariots capable of carrying 8 submarine commandos and explosive charges.
Note: SX-506s are almost indistinguishable externally from SX-756s. The two Colombian boats can be distinguised from one another when their snorkel masts are raised. The ball mechanism on top of Intrepido's mast is flattened, whereas Indomable's is spherical. Both are distinguishable from South Korea's SX-506s by the step mounted around the sail, which is absent on the Korean units. Colombia's SX-506s are sometimes referred to as SX-506/B as a result of their lengthening, however this designation is not used by the Colombians, who usually refer to them as "Submarinos Tacticos."

Key to drawing:

1. Draft marker (painted);  2. diver lockout; 3. crew and passenger quarters; 4. forward battery pack; 5. permanent ballast (8 concrete blocks); 6. fuel and water ballast tanks; 7. control station; 8. large sabotage mines (6x 300 kg mines); 9. aft battery pack; 10. diesel service fuel tank; 11. diesel engine; 12. electric propulsion motor; 13. hydrophone; 14. rescue bouy; 15. periscope with television camera; 16. access hatch; 17. attack periscope; 18. retracting snorkel mast; 19. small (i.e., limpet) mines; 20. ballast tanks; 21. SDV/torpedo tube attachment points.

Instruments: Hydrocompass, autopilot, two sonars, automatic direction finder, bathythermograph, underwater telephone, radio and satellite communications, optical and television periscopes, navigation console, doppler log, and underwater collision avoidance apparatus.

The SX-756 is a straightforward adaptation of the SX-506, with increased range, endurance and weapons carrying capacity, resulting in a 2.2 meter increase in length.  South Korea and Pakistan are the only two countries known to have operated SX-756s. Cos.Mo.S. fabricated five of these boats on-site in South Korea from prefabricated sections shipped out from the company’s factory in Livorno.  Three more were purchased by Pakistan. In service, Korea’s boats were designated SX-756/K while Pakistan’s were referred to as SX-756/W.  The three Pakistani boats were later upgraded to MG-110/LR (see later entry). 

Intended missions for the SX-756 were largely the same as for Cos.Mo.S’ previous boats, with the additional option of a torpedo attack capability carried as an add-on external tube.       

Crew: 6  plus 8 swimmers. 
1x 200-hp Diesel engine,
1x 55-hp electric motor;
Cruising range on diesel engines, 1600 miles at 6 knots; on the electric motor 60 miles at 4 knots. 
Full speed 8.5kts surfaced,  6kts submerged. 
Displacement: 73 tons surface, 80 tons submerged.
Endurance:  20 days
Dimensions: Length: 25.2 meters (82.68 feet), Beam 2.1 meters

Armament options:
(A)  6x  Mk. 21 bottom-type mines (300 kg explosives), 8x Mk. 11 charges (50 kg of explosives)  and  40x small magnetic mines;
(B)  6x ammunition charge containers with an overall weight of 1800kg;
(C)  2x CE2F/60 (or 100) chariot SDVs  and 8x Mk.11 charges or 8x magnetic mines;
(D)  2x 324-mm torpedo tubes and two spare torpedoes (tube mounted externally in same place as chariots);
(E) 6x Mk.21/W bottom mines (300 kg explosives) and 8x Mk.11/W mines.
The torpedo apparatus and containers, bottom mines are placed on external mounts, the small demolition charges are carried between the casing and upper hull cylinder.


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Friday, June 10, 2011

Developments in Technology of Submarine Warfare During the 20th Century

While the idea of a submersible ship had been around since the Renaissance, the advances in technology required were not seen until the end of the Victorian age. It has been a weapon with conflicting ideas as to its mission and role. The 20th Century saw the submarine brought from a curiosity into a highly effective weapon of war, espionage, and deterrence.

The two primary problems of early submarine development were weapons and propulsion. Early attempts at submarine weapons included limpet mines and spar torpedoes that proved just as dangerous to the attacker as the target; Robert Whitehead developed the first self-propelled torpedo in 1866 (Parish 21-22). This weapon, while adopted for use on both surface ships and from shore, proved particularly well suited for use from a subsurface craft as it made its attack underwater, away from the launching platform, and was fully self-contained.

In the field of propulsion many different systems were attempted. Initially, trials using compressed air and all-battery drives were conducted but this linked submarines to a shore base or a tender ship at sea. The Austrians designed a submarine that could operate its gasoline engine while submerged by it feeding air with a pair of breathing tubes (Freivogel 5); but it quickly became apparent to the early developers that two propulsion systems would be required: one for sailing on the surface and one for submerged operations. Almost universally the submerged drive adopted was the battery and electric motor system, as its operation, unlike compressed air, was fully self-contained and in addition provided electricity for the submarine's equipment.

For surface propulsion a myriad of drives were tried. France tried a steam engine but the air intakes proved cumbersome to close when diving and the heat of the steam engine overwhelmed the crew (Preston 15). The British would ignore these difficulties and went on to develop their own steam-powered submarine class (McCartney, Tony Bryan 16). Gasoline engines were tried by designers in America such as John Holland and Simon Lake (Preston 16-17). Unfortunately, while the gasoline engines provided ample power for both surface travel and charging of batteries, the vapors of the fuel were noxious to the crew and posed a danger of fire or explosion in the cramped confines of a submarine (Century). Safer fuels were quickly developed. Kerosene was tried in Germany; while it proved a safer fuel, allowing for quicker dive times and offered longer range, the large amounts of white smoke it produced as exhaust were not advantageous for a warship that was to rely on stealth (Williamson 4). A German invention provided the answer: the diesel engine. Diesel fuel was safe, compact, relatively clean-burning, and produced sufficient drive power. Ironically, it was others who launched the first submarine powered by a diesel engine as Germany itself lacked the engines in sufficient quantities at the time (Preston 19). Irony notwithstanding, the submarine had now become an effective weapon, it was now a matter of learning how to use it and what for.

Early in the 20th century the preeminent naval power, the United Kingdom looked upon submarines with disdain as a defensive weapon, suitable only for defending one's own harbors. Admiral Arthur Wilson stated they were “Underhand, unfair, and damned un-English” (Preston 17). The idea of a weapon that would attack without warning was considered “unsailorlike” (Century), while submarine crews were considered only one step removed from pirates (Preston 17). Despite the reluctance of the Admiralty, under Admiral Sir John Fisher the Royal Navy became a leader in submarine development. The British “D-class” submarines became the first to be equipped with a wireless telegraph, and the first submarine class to have both a deck gun and diesel propulsion (Cocker 27). The British “D-class” were the prototypical submarine of the era; they were 163 meters long and displaced just under 600 tons. They were armed with one or two 12 lb quick-firing guns and three 18” torpedo tubes. Its twin screws could propel the sub at speeds of up to 14 knots, and carried a crew of 25 (Hutchinson 38). Admiral John Jellico commander of the British Grand Fleet and later First Sea Lord envisioned a class of submarines that would sail alongside the Royal Navy's battle fleet, much like the destroyers of the time. He assumed that his main potential adversary the German Navy, had the same idea. Inconveniently, they had other ideas (Preston 36).

As World War One began the initial targets of Submarines were enemy warships. German submarines called U-boats (a shortened version of the German term Unterseeboot) scored several early victories. On 3 September 1914 U-21 sunk HMS Pathfinder, a British cruiser, she would be the first warship sunk in battle by a submarine in modern times. 19 days later U-9 would sink HMS Aboukir, Hogue, and Cressy, cruisers all, within an hour (Williamson 33, Century). The next month U-9 would sink another cruiser HMS Hawke. With no apparent countermeasures to speak of, the Royal Navy evacuated its anchorage at Scapa Flow for a time (Williamson 34). In January of 1915 U-24 sank HMS Formidable a British battleship, the British response to these U-boat attacks was mostly a passive one; they placed nets, laid mines and dispatched patrols (Williamson 35).

Initially the only defense a ship had from submarine attack would be to charge at it while it was still surfaced in hopes of sinking her with gunfire or by ramming her as she dived; if the submarine dived in time a warship had nothing to attack with. Underwater weapons were needed. At first, militarized fishing boats are used to lay nets that would entangle a U-boat and force it to surface where it could be sunk by gunfire. Then, a line of mines were towed behind a patrol ship in hopes of one of the bombs striking a submerged U-boat. Neither proved very effective in practice. Ships outfitted to look like an unarmed cargo vessels were used to try to lure a U-boat to surface to make a deck-gun attack, which was standard practice at the time since torpedoes were both expensive and somewhat unreliable, as well as being difficult to aim. Known as Q-Ships, these ships were actually heavily armed and/or would tow a British submarine behind them to ambush a U-boat (Owen 22-23). By January of 1916 an effective depth charge was finally deployed to the Royal Navy. Imaginatively designated the “Type D”, it was the first to feature a hydrostatic detonator that would set off the weapon at a preset depth. However, the problem of finding a submerged U-boat to use such weapons on remained (Britain np). Simple hydrophones had been deployed as early as 1915 but these devices were omnidirectional and could only be used if stationary; their used was limited providing warning of a submarine's approach. By 1917 a directional hydrophone was developed that could be used by a ship moving, and by war's end versions that could be used aboard seaplanes were developed (Owen 28, 41).

Naval thinking at the start of WWI focused on the belief that the Navy's role was to engage and destroy its enemy's fleet in a decisive battle, and in May-June 1914 it happened off the coast of Jutland, Denmark in the North Sea. After two days of inconclusive battle the Royal Navy was able to maintain its blockade of the German coast. Following the Battle of Jutland the German High Seas Fleet remained in port rather than risk its expensive battleships and cruisers in another inconclusive battle. Because of German naval inferiority, targets for U-boat attacks quickly changed, Germany, recognizing that Britain being an island separated from its empire, relied on its merchant fleets to survive. Thus merchant ships quickly became a target for submarines.

Submarine attacks on merchant shipping were so effective that the admiralty was forced to take drastic countermeasures. One solution suggested was to have merchant ships operate in a convoys protected by warships, Admiral Jellico and others dismissed this as a defensive tactic unsuited to the offensive mindset Royal Navy (Owen 30). The admiralty proposed using a new type of submarine to hunt U-boats: the R-class. These submarines were designed to be fast and maneuverable underwater, and were equipped with directional hydrophones to find their targets and six torpedo tubes to engage them. These R class submarines would arrive too late for the war and would quickly be forgotten (Owen 27-28, Gardiner et al 93).

As the war went on, the methods in which the Central Powers employed submarines would change, eventually culminating in unrestricted submarine warfare against all merchant shipping in the waters around Europe. Germany, rightly assuming that the US would eventually enter the war in support of the allies no matter what it did, allowed its submarines to attack US merchant ships. This escalation of force, and the efficacy of submarine warfare directed at supply lines, did not go unnoticed.
With merchant shipping losses mounting, the British adopted a convoy system thanks to the advocacy of British Admiral David Beatty and American Admiral W. S. Sims. Sinkings by U-boats dropped dramatically after the adoption of the convoy system (Owen 30-31). Merchant ships in a convoy were protected by escorting warships and it reduced the number of targets the U-boats had from many to one. (Owen 43). Convoys represented the final blow to the German U-boat in WWI, but by war's end U-boats had sunk 12.5 million tons of allied and neutral shipping (Hutchinson 69).

As the war drew to a close, one more weapon would appear. Called ASDIC for Anti-Submarine Detection Investigation Committee by the British (today this is referred to as Active Sonar), this detection device would transmit an acoustic pulse into the water called a 'ping' that would bounce off a submarine and be detected by the hydrophones giving an attacking ship both a bearing and range on its target. The British assumed that this sensor along with depth charges would render the submarine ineffective in future wars. (Owen 42).

As the world's nations rebuilt following WWI their navies analyzed the results of submarine operations and designs of the war. In the United States, whose submarines had played almost no role in the war, a schism formed between two factions of the naval service with regards to submarine design; one side wanted a submarine similar to the best submarines of the last war, albeit larger, and the other faction wanted a long-range submarine that could operate in the Pacific and be fast enough to operate alongside the fleet. The debate continued for ten years before a consensus was reached. US submarines would be the long-range "Fleet Boats". Two officers who played critical roles in advocating this position would later be known for their service in WWII, they are Charlies A. Lockwood and Chester W. Nimitz (Parrish 187, Century, Crozier np). The development of Fleet Boats in the interwar years reached a pinnacle in 1940 with the Balao class submarine. The Balaos were 311 feet long and displaced 2,424 tons. Armed with an assortment of guns and ten torpedo tubes these submarines could operate 12,000 nm from base and reach speeds of over 20 knots (Hutchinson 101). The Balaos and its derivatives the Gatos and Tenches would be the US Navy's workhorses in the Pacific war. On the other side of the Atlantic, a re-arming Germany established front companies in other nations that produced designs for new weapons including submarines to circumvent the restrictions of the Treaty of Versailles. Countries contracted German front firms like IvS to conduct design studies for their own submarines; information from these studies were used to develop new classes of German U-boat that were laid down after Germany and Britain had renegotiated Germany's naval restrictions (Westwood, David 8).

Tactics of submarine employment changed following WWI. In Germany the practice of commerce raiding and submarine warfare became an accepted naval doctrine, an understandable stance when considering that one's primary opponents wield the world's most formidable surface fleets. However, the success of the U-boats and their "course-de-guerre" did not teach a universal lesson. The United States integrated submarine operations with surface fleet operations, employing them as scouts and skirmishers. Japanese submarine doctrine was to use them to snipe at an advancing enemy force and ignored the potential of an anti-shipping campaign (Carpenter, Dorr, and Polmar 1).

When the second world war broke out submarines were once again in action on both sides with the German submarine U-30 sinking the passenger ship SS Athena within hours of the start of hostilities. On 17 September 1939 U-29 sank the aircraft carrier HMS Courageous and on 14 October 1939 U-47 penetrated the defenses around the British naval base at Scapa Flow and sank HMS Royal Oak, a battleship while she sat at anchor. Before war's end the British carriers HMS Ark Royal, Eagle, Audacity, Avenger, the battleship HMS Barham and the American carrier USS Block Island would join them (Most np). The losses among merchant shipping were even more devastating with nearly 3,000 ships sunk. For the allies in the European theatre submarines became a weapon to isolate the Axis. For example, HMS Upholder sank the Italian troopship SS Conte Rosso on 24 May 1941 costing the Italians 1,300 troops headed for North Africa. Also, allied submarines would exact a toll on the
German U-boats sinking 22 of them (U-boats np).

Early in the Battle of the Atlantic German U-boat were able to exploit a weakness in the Allied ASW (Anti-submarine warfare) tactics. The Allies, the British in particular focused on using ASDIC to detect hostile submarines, the Germans chose to instead attack surfaced at night so ASDIC would be unable to detect them and lookouts on ships would be unable to see them except at close range. The Allies began to counter this tactic by fitting escort ships with radar sets that could detect a surfaced U-boat. Aircraft were also fitted with radar sets allowing for the Allies to search large areas for submarines.

As the war spread to the Pacific the submarine would be in combat from beginning to end. When the Japanese Navy attacked Pearl Harbor it dispatched a force of five midget submarines transported to the target area on the deck of a larger sub. One of these midgets became the first Japanese warship to be sunk. In the hours before the attack the destroyer USS Ward spotted one attempting to enter Pearl Harbor and sank her. Two of these midgets successfully entered Pearl Harbor and one may have attacked the battleship USS Oklahoma (Reich np).

With the virtual destruction of the US battleship force in the Pacific the only intact forces left were the USN's carriers and submarines. Given the almost total Japanese naval superiority over most of the Pacific, US submarines became the only ships that could strike deep in Japanese waters. However, a score of technical problems plagued early US submarine operations from the outset. Principal among these were the inadequately tested torpedoes issued to the fleet. The lack of prewar tests of the Mk 14 caused several faults in the weapon to not be known until the war broke out (Newpower, Anthony 30). The major faults in the weapon were its inability to change depth, a faulty contact detonator, and an unreliable magnetic detonator (Newpower, Anthony 15, 103, 106-108). The wartime Mk 18 introduced circular running problems to US torpedoes, when the rudder tended to jam occasionally, which caused the weapon to simply circle back to the launching submarine. (Newpower, Anthony 219). When combined these faults made for largely ineffective weapons, even hazardous ones for the sub given the tendency for failed detonation (failed detonators do not fail to alert the target ship) and faulty guidance that caused two subs to be struck by their own torpedo (Hutchinson 111). The faults in weaponry were clearly demonstrated; at the start of the war in the Philippines the US Navy had stationed its largest force of submarines; consisting of 29 boats of the S, P, and Salmon classes, in the area (Blair, Clay 82). However, these submarines only sank three ships out of 45 attacks made (Spector, Ronald H. 130). By the time the Philippines was fully conquered by the Japanese the Asiatic Fleet submarines had sunk just 10 ships and lost four of their own in return. The redesign of the Mk 14 and improvements to the electric-powered Mk 18 slowly solved these problems and by the end of the war the US Submarine Service had sunk approximately 4,000 Japanese ships displacing some 10 million tons (Parrish 423).

In regards to the opposing forces, the Japanese were highly innovative in submarine design. They built many large submarines capable of long-range patrols, submarines capable of carrying seaplanes for reconnaissance or strike missions and several classes of high-speed submarines. However, their submarine force accomplished very little due to its rigid doctrine of using submarines as scouts to locate and trail Allied naval task forces and not to hunt slower supply convoys. This warship only approach was critically flawed in that surface warships were faster and more maneuverable in comparison to the submarines of the time. By the end of the war the suicidal nature of Japanese resistance spread underwater; the Japanese Navy developed a torpedo-shaped submarine that could be piloted by a person. These human torpedoes, called "Kaiten", could, in theory, approach a target and guide itself into the target. Unfortunately for the Japanese, the crude nature of the weapon's design
combined with its late introduction resulted in very little accomplished.

Returning to the European Theater; the battle of the Atlantic was turning against the Axis. The Allies had developed several effective countermeasures to the U-boats. Strategically High Frequency Direction Finding stations were established on land and warships were equipped with smaller versions. This system allowed the Allies to intercept and triangulate radio signals from U-boats to their bases ashore. By locating the areas where U-boats were operating convoys could be routed around them and warships directed to them. On the tactical level the Allies had developed a series of weapons and sensors to combat U-boats. Aircraft were now equipped with on board radars capable of detecting a surfaced submarine and expendable Sonar Buoys that could locate a submarine after it had submerged and their payload's now included acoustic homing torpedoes. The U-boats were slowly forced to remain dived or risk bombing by Allied patrol planes, the current generation of U-boats were slow while dived and could only travel a short distance. A new type of submarine would be needed if the Germans were to continue the war in the Atlantic.

In 1936 German engineer Helmuth Walter presented a plan to the German navy for a new type of submarine that would remain submerged for its entire patrol and be capable of unheard underwater speeds. In 1940 his experimental V-80 was launched, powered by a High-Test Peroxide (HTP) burning turbine the submarine could reach speeds of 26 knots and just as importantly could operate the turbine while submerged. It was hoped that such a submarine would be able to avoid the Allied countermeasures to the current generation of U-boats (Polmar, Kenneth J. Moore 2-3). Plans were drawn up in 1942 for the Type XVII class U-boat, a combat capable derivative of the V-80 (Miller, David 75). These submarines could operate at speeds of 20 knots for up to 5 hours; twice as fast and five times longer ranged than the best Allied submarine class (Polmar, Kenneth J. Moore 33-35). The cutting edge technology of the Walter Turbine proved unfeasible because of the dangers associated with the handling of the fuel in the confined spaces of a submarine and the cost of manufacturing the fuel. However, the hull design of the Type XVII was highly improved over the current generation of U-boats (Miller, David 76). A submarine that used the Type XVII's streamlined hull design but was driven by a conventional albeit highly capable electric motor system was designed, called the Type XXI these submarines showed the way forward in submarine development. (Miller, David 61)

The Type XXI U-boat was designed to spend its entire patrol (over 17,000 miles) submerged. Such operational capability was achieved by use of a snorkel that allowed the running of the submarine's diesel engines while submerged. On battery power the submarine could achieve speeds of 16 knots for short periods or travel up to 325 miles at 6 knots before needing to charge her batteries. The Type XXI's offensive capability was provided by six torpedo tubes and 23 acoustically guided torpedoes capable of being fired from depth below periscope depth, for defense the sub had four 20 or 30mm anti-aircraft guns (Jackson 81).

Following the end of WWII the Allies split the captured German Kriegsmarine, Italian Regia Marina and Imperial Japanese Navy submarines among the various victorious nations. German Type XXI U-boats were transferred to The US, Britain, The Soviet Union, and France. Several small but advanced German Type XXIII U-boat are transferred to Britain, the Soviet Union and Norway. Two surviving Type XVII Walter U-boat were split between the US and Britain, while data on Walter's work was captured by the Soviets. In the Pacific the US captured several large aircraft carrying submarines of the Japanese I-400 class were quickly studied and then scuttled to avoid having to allow the Soviets to gain access to the technology (Sakaida et al. 66-68, 85-86).

German U-boat technology became the basis of post-war submarine development. All the major powers took note of German designs for their own submarines. The United States, with its impressive submarine fleet, though now obsolete (Friedman, Norman. 3), began construction of new Type XXI style submarines (The Tang class). To fill the gap in new submarine construction WWII vintage submarines were heavily modified as part of the GUPPY program. Hulls and superstructures were now streamlined, deck guns removed. Better propulsion systems were installed as well as larger sonar arrays. The GUPPY upgrades kept these old subs in service with the USN and other navies for an impressive time period. Other nations such as Britain followed suit and modified their WWII vintage submarines to such standards (Lambert, and David Hill 18-21).

New technologies produced a radical shift in submarine operations, during WWII radar was the primary electronic detection system of the submarine. Its use was, of course, limited to when the submarine was surfaced or at periscope depth. Sonar use at the time was focused on tracking of a contact already detected, mainly to avoid attack by an enemy ASW vessel. In the 1950s sonars became advanced enough to extract the low-frequency acoustic signals (signals in the 50-150 HZ range) from the broadband noise generated by a ship, this is known as LOFAR. With LOFAR, submarines could detect contacts at further ranges (low-frequency sound waves travel farther), and with analysis determine the type or even class of a contact based on the different low-frequency signal spikes (called tonals) created by a contact's machinery (Friedman, Norman 66). With the shift in sensors focused now on sonars tracking of a target became a more complex affair, with radar detections a contact's bearing and range were known, passive sonar provides only bearing to a target and the Doppler shift of the target. By analyzing these two factors though a series of maneuvers a target's range, course and speed became known (Clancy, John Gresham 70). Submarine maneuvers now would be centered around localization and not just detection of targets.

The Soviets incorporated German design features into a submarine class already on the drawing board. The Project 613 or WHISKEY class boats were constructed in prolific numbers; 236 vessels of seven subclasses were built before production was halted (Polmar 118). The perceived rapid development of Soviet snorkel boats caused a major shift in design and tactics by the western powers. The current generation of sensors and weapons were not designed to fight snorkel submarines, a new approach was needed. The submarine itself became the answer; submarines by nature are capable of spending long times on station undetected whereas a surface ship is easily detected and aircraft must return to base every few hours. The USN took several GUPPY submarines and installed a LOFAR sonar designed partly on captured German technology and capable of detection of snorkeling subs at ranges of up to 30 NM (Friedman, Norman. 13, Cote, Jr., Owen R. np). These submarines became the first Hunter-Killer boats or SSKs. Combat capability was provided by a new series of torpedoes the Mk 35 (for offense) and Mk 37 (for self-defense), the Mk 35 and Mk 37 torpedoes were able to engage all known or planned submarine classes; although the smaller Mk 37 became the preferred torpedo due to its wire-guidance capability, which was greatly improved on the Mk 37 Mod 1 weapons. These added the ability for the operator to steer the torpedo towards the target's predicted location (Friedman, Norman. 19-20).

The Walter turbine technology was developed further in the UK and USSR. Two submarines were constructed for the RN: HMS Explorer and HMS Excalibur. Both were conceived as testbeds for the new engine (Cocker 106). Following the loss of 13 crew members of HMS Sidon to a HTP torpedo fuel explosion further development of the Walter turbine was mostly abandoned in the west until the 1990s (Roll of Honour np). In the east the Soviets produced a single vessel that was driven by a Walter turbine type engine. Given the NATO reporting name WHALE, she was capable of very high speeds for its time. Following an on-board power-plant explosion, the submarine was decommissioned and further development abandoned (Polmar, Kenneth J. Moore 42). HTP would remain in use as torpedo fuel by Russia until the early 2000s when due to the lost of the Submarine Kursk in 2000 the Russian navy would remove it from service (Weir, Walter J. Boyne 244). Non conventional submarine propulsion would take a different route.

Modified WWII era submarines and copies of Germany technology showed a marked improvement over the war era submarines but new technologies would soon supplant them. In 1954 the USS Nautilus SSN 571 was commissioned. Nautilus combined the Tang class hull, weapons and sensors with a nuclear propulsion system (Polmar, Kenneth J. Moore 57). Nuclear power not only increased the speeds a submarine was capable of but removed the need to surface or snorkel to recharge batteries. With her high-speed and advanced weapons Nautilus dominated naval war games (Century). But another technological development would join nuclear power to create an even deadlier warship. A year before Nautilus was commissioned an experimental submarine named Albacore AGSS-569 was put into service; she featured a teardrop-shaped hull and a single propeller. This hull shape allowed for even higher speeds in excess of 40 knots. It became apparent that a nuclear powered submarine with a teardrop hull would be desirable, so the Skipjacks and Thresher/Permits became these warships (Polmar, Kenneth J. Moore 132-133). Following suit, the Soviets would soon built their own SSNs, a nuclear undersea arms race had begun and the submarine would soon take on new forms and roles such as that of missile carrier.

The Permit-class submarines (use of the name Thresher-class was abandoned after the loss of the lied ship of the class in 1963) became the baseline configuration for all US submarines to follow until the 1980s. The Permit class was highly capable, she could dive to depths of 1,300 feet (The Tangs could submerge to 700 feet), she was fast at 28 knots, her machinery incorporated the latest quieting features, also her weapons and sensors were cutting edge (Polmar, Kenneth J. Moore 147-148). The Permits became the first submarines armed with SUBROC (SUBmarine ROCket), based on the large detection ranges capable with modern sonar the ability to strike a target ship at ranges measured in the 10s of miles led to the development of a guided rocket fired from a submarine's existing torpedo tubes. The UUM-44 SUBROC flew on a ballistic trajectory and delivered a tactical nuclear warhead to a preset depth (Polmar, Kenneth J. Moore 149).

Starting in the late 1950s, US SSNs now had a new target: Soviet submarines capable of launching nuclear missiles (Polmar, Kenneth J. Moore 109-111). The threat of nuclear attack against the United States made tracking Soviet missile submarines a priority. The early model Soviet submarines were easy to track by NATO forces as was demonstrated during the Cuban Missile Crisis where US forces were able to track four Soviet nuclear armed FOXTROT class submarines using SOSUS and Boresight direction finding stations (Reed np). By 1967 the Soviets finally developed a submarine class closer to the US Polaris missile submarines designated YANKEE by NATO, however US submarines still had a qualitative edge over their Soviet counterparts well into the late 1970's (DiMercurio 8).

Production of Permit-class subs ended and Sturgeon-class submarines began. The Sturgeons maintained the basic design of the Permits although slightly larger and fitted with more up to date equipment. With 37 boats of this class built, the first commissioned in 1967 the Sturgeons were the backbone of the US submarine force until the introduction of the 62 boat strong Los Angeles class. Echoing their cold war role as spy subs the Sturgeons were fitted with extensive electronic and acoustic eavesdropping gear (Polmar, Kenneth J. Moore 154,-155). One sub of the class; USS Parche SSN-683 was lengthened 100 feet to make room for additional gear. This submarine took part in the secret cable-tapping missions conducted against the Soviets in a Pacific operation code-named "Operation Ivy Bells" (Sontag et al 297). Information gathered on these missions gave new insight into Soviet naval operations that could not be gathered otherwise, and in 2004 the Parche ended her career as the most highly decorated warship in the history of the United States Navy (Reed np).

The Soviets, at this time, took a different track in submarine design and employment. Soviet naval doctrine saw US Aircraft Carriers as their primary threat to the Soviet motherland (Platonov 2). Development of a high-speed submarine capable of intercepting US carriers before they were in range of Soviet targets was a priority. In a radical departure in Soviet submarine design the Project 704 ALFA class submarine is put into production. It was designed to incorporate new technologies such as a titanium hull (previously tested on the one-off PAPA class), a liquid sodium cooled reactor, and extensive automation (Polmar, Kenneth J. Moore 140-141). Capable of speeds of 41 knots and with a test depth of 1,300 feet they were for a time the fastest and deepest diving production submarines in service making them basically untouchable to the current generation of NATO ASW weapons. The high performance of these submarines led NATO to develop new weapons and countermeasures including high-performance torpedoes like the US Mk 48 and British Spearfish (Polmar, Kenneth J. Moore 142-143, Thamm np).

In 1967 a former US Navy warrant officer named John Anthony Walker approached the Soviets at their Embassy in Washington and sold them a navy cypher card for several thousand dollars. Until his arrest for espionage in 1985, Walker fed the Soviets with information on USN communications (Reed np). The Soviets learned that NATO forces were able to track and trail their submarines with ease. This knowledge would change Soviet submarine design as the their next generation of nuclear submarines were put into production. Between 1980 and 1984 the Soviet Union launched subs of seven separate classes of submarine: OSCAR, KILO, TYPHOON, MIKE, SERRIA, AKULA and DELTA (Polmar, and Kenneth J. Moore 278). These new classes represented a shift in Soviet submarine design, these subs were not only faster and could dive deeper than their American counterparts they had quieting levels approaching that of US submarines. They were the first Soviet submarines fitted with digital sonars and were armed with more advanced weapons such as a Russian version of the SUBROC (Polmar, Kenneth J. Moore 285, 297-298, Wertheim 596).

The varied construction of Soviets submarines can be sharply contrasted with the singular focus of US Submarine construction. US sub construction in the 1980s focused on one class of attack sub (Los Angeles) and one class of missile sub (Ohio) at a time. One reason for this focus was the lack of a weapon that needed its own class of submarine to deliver it. All US submarine weapons (aside from ballistic missiles) could be launched from a submarine's torpedo tubes, while the Soviets developed larger tactical missiles that required their own separate launcher. Additionally the dual production of Soviet submarine types can be attributed to a shift in naval design. Beginning with the ALFA class of the 1970's the Soviets experimented with titanium for submarine hulls. Titanium has greater stregth per pound than steel allowing a lighter submarine to perform at the same level as a heaver submarine (Polmar, and Kenneth J. Moore 281-282). The SERRIA class and the one-off MIKE utilized hulls made of Titanium, these submarines had depth and speed performances well ahead of their US counterparts. However, the difficulty of building titanium submarines of that size resulted in only four SERRIA class subs being commissioned. A steel-hulled derivative of the SERRIA was desirable, this vessel became the Project 971, NATO code name AKULA. The AKULA maintained SERRIA level performance by an increase in displacement while allowing for construction of a larger number of subs (Polmar, Kenneth J. Moore 284).

Advances in submarine design remained mostly untested in battle after World War II. There was a submarine attack in the Indian Pakistani war of 1971, the Pakistani submarine PNS Hangor attacked and sank an Indian navy frigate (Bharat np). In 1982 the Falklands war between Argentina and the United Kingdom involved large-scale naval forces of both including submarines. On the British side five nuclear and one conventional submarines were deployed. Argentina deployed two conventional submarines. The British SSN HMS Conqueror trailed an Argentine task force formed around the ARA General Belgrano; a WWII era cruiser. Conqueror sent the cruiser to the bottom with a spread of three torpedoes (Hastings, Simon Jenkins 149). The Argentine response to the sinking proved decisive for the British; The Argentine fleet, including its aircraft carrier, was recalled to port: they simply had no defense against a nuclear submarine (Hastings, Simon Jenkins 157). Argentine operations met with far less success. ARA Santa Fé a GUPPY type submarine was forced to the surface by several RN helicopters and subjected to repeated attacks before the crew abandoned ship, the ARA San Luis made repeated attacks against British forces including several warships and a submarine according to one source; but due to a malfunctioning control system and defective torpedoes they failed to hit any targets (Sciaroni, J. Matthew Gillis. 27).
As the 20th century came to an end and the 21st began strikes against targets ashore became one of the more visible missions of the submarine. In 1991, 1998, 2002, 2004, 2011 USN and RN submarines launched Tomahawk cruise missiles against targets in Iraq, Serbia, Sudan, Afghanistan and Libya (Dwyer, Devin, and Luis Martinez np, BGM-109 np). Covert operations also continued, one that has come to light is the trailing of the Chinese freighter An Yue Jiang by a British nuclear submarine. The Chinese freighter was bound with a cargo of weapons for Zimbabwe in 2008. This trail proved crucial to the British government's diplomatic success in blocking the freighter from reaching its destination (Mangena np). In March of 2010 the South Korean corvette ROKS Cheonan was sunk with the loss of 47 sailors apparently a victim of a North Korean submarine's torpedo (Yoon et al. 89).

In the past century the submarine had gone from a cantankerous craft with an unclear mission to a centerpiece of national defense. The glorified sewer pipes of WWI slowly transformed into the lean gray wolfs of WWII and finally into the high-tech warships of today. Continued leadership in submarine development is critical for any nation that intends to exercise its power at sea as can be seen in the recent surge of submarine construction in the developing world, with countries such as China, India and Iran producing large numbers of submarines for their respective navies (Eaglen, Mackenzie np, Iran np, NTI np). Successful use of these underwater weapons will be critical in any naval war in the 21st century.

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