Allied submarines were used extensively during the Pacific War and were a key contributor to the defeat of the Empire of Japan. A total of 283 allied submarines were active in the Pacific and Southeast Asia between 1941 and 1945, of which 61 were sunk.de Bles, Boven and Homburg (2006), p. 74.
During the war, submarines of the United States Navy were responsible for 56% of Japan's merchant marine losses; other Allied navies added to the toll. The war against shipping was the single most decisive factor in the collapse of the Japanese economy. Allied submarines also sank a large number of Imperial Japanese Army (IJA) troop transports, killing many thousands of Japanese soldiers and hampering the deployment of IJA reinforcements during the battles on the Pacific islands.
They also conducted reconnaissance patrols, landed special forces and guerrilla troops and performed search and rescue tasks.Blair, Clay, Jr. Silent Victory (Bantam, 1947), pp.508, 521–2, 568, 574, 576, 609, 646, 724, 745–6, 784, 806, 818, 825, 827, 829, 842, 865–6, & 868–9. The majority of the submarines involved were from the U.S. Navy, with the British Royal Navy committing the second largest number of boats and the Royal Netherlands Navy contributing smaller numbers of boats.
The Allied submarine campaign is one of the least-publicized feats in military history, in large part because of the efforts of Allied governments to ensure their own submarines' actions were not reported in the media. The U.S. Navy adopted an official policy of unrestricted submarine warfare, and it appears the policy was executed without the knowledge or prior consent of the government.Holwitt, Joel I. "Execute Against Japan", Ph.D. dissertation, Ohio State University, 2005, pp.212–217 & 232–249 passim. The London Naval Treaty, to which the U.S. was signatory,Holwitt, passim. required submarines to abide by prize rules (commonly known as "cruiser rules"). It did not prohibit arming merchantmen,Holwitt, p.6. but arming them, or having them report contact with submarines (or raiders), made them de facto naval auxiliaries and removed the protection of the cruiser rules.Dönitz, Karl. Memoirs: Ten Years and Twenty Days; von der Poorten, Edward P. The German Navy in World War II (T. Y. Crowell, 1969); Milner, Marc. North Atlantic run: the Royal Canadian Navy and the battle for the convoys (Vanwell Publishing, 2006) This made restrictions on submarines effectively moot.Holwitt, p.6.
Background The U.S. had the largest and most powerful submarine force of all the Allied countries in the Pacific at the outbreak of war. Pre-war U.S. Navy doctrine—like that of all major navies—specified that the main role of submarines was to support the surface fleet by conducting reconnaissance and attacking large enemy warships. Merchant ships were regarded as secondary targets, and the circumstances in which they could be attacked were greatly limited by prize rules set out in the London Naval Treaty, to which the U.S. was a signatory.
The U.S. Navy built large submarines which boasted long range, a relatively fast cruising speed and a heavy armament of torpedoes. United States submarines were better suited for long patrols in the tropics than those of the other major powers due to amenities such as air conditioning (which German U-boats, for instance, lacked) and fresh water distillation units. The submarines' commanders and crewmen were considered elite and enjoyed a strong esprit de corps.Spector (1984), pp.480–483. On 7 December 1941, the USN had 55 fleet- and 18 medium-sized submarines (S-boats) in the Pacific, 38 submarines elsewhere, and 73 under construction.Morison (1949), p.188. (By war's end, the U.S. had completed 228 submarines.)Lenton, H. T. American Submarines (Navies of the Second World War Series; New York: Doubleday, 1973), p.5 table.
While Britain stationed a force of submarines in the Far East prior to the outbreak of war, no boats were available in December 1941. The British had 15 modern submarines in the Far East in September 1939. These submarines formed part of the China Station and were organised into the 4th Flotilla. Although the number of British submarines in the Far East increased in early 1940 when the 8th Flotilla arrived at Ceylon, both flotillas and all their submarines were withdrawn in mid-1940 to reinforce the Mediterranean Fleet.Mars (1971), pg 27, 62 and 64.
The Netherlands also maintained a submarine force in the Far East in order to protect the Netherlands East Indies (NEI). In December 1941, this force comprised 15 boats based at Surabaya, most of which were obsolete.Mars (1971), pg 212.
Strategic implications Throughout the war, Japan was dependent on sea transport to provide adequate resources, including food, to the home islands and supply its military at garrisons across the Pacific. Before the war, Japan estimated the nation required of shipping to maintain the domestic economy and military during a major war. At the time of the attack on Pearl Harbor Japan's shipping capacity was much greater than that, totaling of shipping: the Japanese merchant fleet was capable of , and smaller craft were capable of an additional . Parillo (1993), pg 37–38.
Despite an awareness that shipping was vital, the Japanese navy seriously underestimated the (eventual) threat from Allied submarines. Anti-submarine warfare was accorded a low priority and few warships were allocated to protecting merchant shipping, while aircraft were rarely used.Parillo (1993), pg 63–73. Japanese destroyers formed the bulk of convoy protection; they had impressive night fighting capabilities with powerful surface armament of guns and torpedoes, but had deficiencies in sonar and radar compared to equivalents of other navies.Japanese Destroyers Moreover, Japanese Navy doctrine in relation to commerce defense was very bad.Parillo; Peattie & Evans, Kaigun. This overconfidence was reinforced by the ineffectiveness of Allied submarines in the early part of the war, in particular due to the U.S. submarines being led largely by timid skippers and being equipped with faulty Mark 14 torpedoes. While the Allies in the Atlantic had to ramp up their shipbuilding capability quickly to replace the large number of ships sunk by German U-boats in the Atlantic theatre, the initial low losses of Japanese ships in the Pacific meant that Japanese shipbuilding faced no immediate urgency to increase production.Parillo.
The size and effectiveness of the Allied submarine force increased greatly during the Pacific War. The U.S. increased production of modern submarines from 1942 onward. The efforts of Admiral Charles A. Lockwood were crucial for the rectification of the Mark 14's problems which were finally resolved in September 1943. Lockwood also selected more aggressive submarine skippers. Signals intelligence broke the "maru code" in January 1943, after a gaffe by U.S. Customs pre-war had caused Japan to change it,Blair; Farago, Broken Seal. and American aircraft engaged in aerial minelaying in Operation Starvation. As a result of all of these developments, U.S. submarines suddenly inflicted devastating losses on Japanese merchant shipping in 1943 and 1944, which caught Japanese military planners off-guard as they lacked the industrial capacity to replace ships that were sunk, and by January 1945 the Japanese merchant fleet was effectively destroyed.Blair, pp.819 & 967ff.
Countering the Japanese offensive (1941-42) In a break with pre-war doctrine (which, like Japan's, had presumed a rush across the Pacific and a "decisive battle" between battleships), with the London Naval Treaty, and with long-standing U.S. defense of freedom of the seas, U.S. naval commanders in the Pacific were ordered by the U.S. Navy Chief of Staff to "execute unrestricted air and submarine warfare against Japan" on the afternoon of 7 December 1941, six hours after the Japanese attack.Spector (1984), pp.478–479; Blair, Silent Victory, p.106; Holwitt, Joel I. "Execute Against Japan", Ph.D. dissertation, Ohio State University, 2005.(page needed). This order authorized all U.S. submarines in the Pacific to attack and sink any warship, commercial vessel, or civilian passenger ship flying the Japanese flag, without warning. Thomas C. Hart, commander in chief, U.S. Asiatic Fleet, issued the same order at 03:45 Manila time (09:15 in Hawaii, 14:45 in DC) on his own initiative (but knowing U.S. Navy Chief of Operations Harold "Betty" Stark intended to do so).Holwitt, Joel I. "Execute Against Japan", Ph.D. dissertation, Ohio State University, 2005, pp.212–217 passim.
The Pacific Fleet submarine force had emerged unscathed from the attack on Pearl Harbor and departed on the fleet's first offensive war patrol on 11 December. The Asiatic Fleet's 27 submarines (including more fleet boats than at Pearl Harbor)Blair, Silent Victory. also went into action on the first day of U.S. involvement in the war, beginning war patrols in the waters around the Philippines and Indochina.Christley (2006), p.39. Due to inadequate prewar planning, which made no provision for defensive minelaying,Willmott, H. P. Barrier and the Javelin? nor for placing submarines on station around the Philippines,Blair, Silent Victory, pp.157–158. nor off enemy harbors,Blair, Silent Victory, pp.156–8. the Asiatic Fleet's efforts to counter the Japanese invasion of the Philippines were unsuccessful and the fleet's surviving submarines were forced to withdraw to Surabaya in the Dutch East Indies (DEI).Morison (1948), p.303.
British, and U.S. submarines took part in the unsuccessful defense of British Malaya and the DEI in late 1941 and early 1942. In December 1941, five Dutch submarines attacked the Japanese invasion fleet off Malaya. These submarines sank two Japanese merchant ships and damaged four others, but three of the attackers were sunk. The two surviving Dutch submarines were withdrawn to defend the DEI, where they were assisted by two British submarines, which had been transferred from the Mediterranean Fleet, and several U.S. boats.Mars (1971), pp.211–213. The U.S. Asiatic Fleet's submarine force left Surabaya for Fremantle, Western Australia, on 1 March. (They would remain in Australia, on the most hazardous and unproductive stations for U.S. submarines, for the duration.) By this date, the Asiatic Fleet's 27 submarines had sunk 12 Japanese ships for the loss of four U.S. boats.Morison (1948), pp.303–305. Following the fall of the DEI, only a handful of British and Dutch submarines were based in the Indian Ocean, and these had little impact on Japanese forces in the area.Mars (1971), pp.214–215.
After the Battle of the Coral Sea, the U.S. Navy detached eight submarines to finish off the damaged aircraft carrier , but she evaded all of them. At the Battle of Midway, although the attack on the battleship by had been unsuccessful, it drew the destroyer Arashi temporarily away from the main fleet to drop depth charges, and the destroyer's return was traced by 's VB-6 to the Japanese task force, where the dive bombers promptly set on fire the fleet carriers Akagi and Kaga.Bicheno, Hugh. Midway (Sterling Publishing Company, 2001), p.134.Lord, Incredible Victory p. 213; Parshall & Tully, Shattered Sword, pp.302–303.
In 1942, the only significant warships that U.S. submarines had managed to sink were the heavy cruiser and the light cruiser .
Reasons for ineffectiveness At the start of the war, the U.S. submarine fleet was ineffective, for multiple reasons:Blair, Silent Victory, p.439. A high proportion of the submarines deployed against the Japanese were obsolete. U.S. boats were hampered by defects in their primary weapon, the Mark 14 torpedo. Poor training led to an excessive reliance on sonar. Skippers were insufficiently aggressive,Blair, Silent Victory, pp.361, 553, & passim. and they exhibited an undue fear of destroyers' sonar and aircraft.Blair, Silent Victory, p.156.