Appendices - Hirohito's War
APPENDIX A: SUBMARINES - THE UNDERSEA WAR
The Failure of Japanese Counter-Submarine Strategy: At the start of the Asia Pacific War, the Japanese Navy was equipped with some of the best attack destroyers of the war. The first Fubuki Class destroyer launched in 1926 set a world class standard for its speed and weaponry. Apart from the top heavy Hatsuhara Class destroyer, designed to comply with the 1930 London Naval Treaty, the Japanese Navy produced a series of superb destroyers; the Shiratsuyu Class was a quickly developed re-design to correct the problems of the Hatsuhara Class. However when Japan allowed the 5-year provisions of the London Naval Treaty to lapse, the Asashio Class destroyer was developed with a speed of 35 knots and a range of 10,600km. It could also carry six 127mm naval guns as well as up to 28 Type 96 AA guns, 16 torpedoes and 36 depth charges.
Further offensive destroyers were developed with the Kagero Class, the Yugumo Class and Akizuki Class destroyers that were introduced between 1939 and 1942. Armed with Long Lance torpedoes, these Japanese destroyers became feared offensive weapons. But they had shortcomings. Apart from the weakness of their radar systems, the main concern was their over-sophistication. They were also designed to fight as auxiliary offensive vessels in large surface actions. By the end of 1942 it became clear that this was not the pattern of naval warfare that could now be expected. As aircraft came to dominate naval engagements, Japan’s overly complex destroyers were exposed as weapon systems that were too costly and time consuming to build.
By 1942 the Imperial Japanese Navy realized that it needed mass-produced destroyers of a lower specification and with greater emphasis on anti-aircraft artillery for the protection of fleet carriers, and more depth charges for deployment against US submarines. The result was the development of the Matsu and Tachinbana Class destroyers that were slower with a speed of 27 knots but carried more anti-aircraft and depth charge firepower. However by the end of the war only 42 out of 122 vessels planned had been built.
Perhaps not surprising in view of the offensive mentality of Japan’s Navy, the attention paid to convoy strategy and protection was de minimis. Despite the urging of Navy Chief of Staff, Admiral Kanji Kato, in a memo written in 1929 regarding the importance of protecting sea-lanes, scant attention was paid to this aspect of any future war. Experts within naval intelligence, such as Lieutenant-Commander Atsushi Oi, who had studied the British convoy system in 1939, were ignored by their superiors. The issue was also raised by the Cabinet Planning Board in 1941 but was deflected by Admiral Osami Nagano’s bland assurances that the Navy was dealing with the problem of bringing “American submarines under control.”30 Until late in the war there was no convoys plan or any one naval or military authority in sole charge of organizing the protection of foreign supply - an extraordinary oversight given that access to commodities, particularly oil, was the casus belli. It was an oversight that Germany’s naval attaché in Tokyo, Vice-Admiral Paul Wenneker, found particular irksome. He recorded that he “suggested the desirability of attacking the route between Honolulu and the West Coast because that would force the use of convoys and would force the withdrawal of many escorts from the western Pacific.”31 Wenneker organized for a full submarine crew to be sent to Germany for special training on German attack methods but on the return journey their submarine was sunk.
Reflecting this oversight on convoys, at the start of the Pacific War, Japan had a paucity of escort destroyers or Kaibokan (ocean defense ships). These vessels, designed to travel at less than 20 knots because they were protecting slower moving cargo ships (10 -15 knots) were armed primarily with depth charges (up to 300) and anti-aircraft guns. For the whole of Japan there were just four Shimushu Class escorts and a smattering of older vessels. Of their successors that were commissioned after the outbreak of war, the Etorofu Class had just 14 ships built while of the later planned mass-produced Ukuru Class there were only 29 built of the 142 planned. It was too little, too late.
Lockwood’s forces were also helped by the paucity of Japanese sonar devices and their failure to develop forward throwing mortar depth charges. Unlike their Japanese counterparts, US submarines were all fitted with SD non-directional anti-aircraft radar by the end of 1942. US submarines were also equipped with SJ surface radar by the end of the following year. As well as providing accurate direction radar information regarding incoming aircraft, even when they were low flying, SJ radar could send point-to-point signals between submarines operating in a wolf pack. Revolutionary PPI (Plan Position Indicator) screen technology was also introduced. As for periscopes, Lockwood’s Submarine Force was up-rated in 1944 from which time periscopes were manufactured with range finding ST, SD or DSJ radar built in. This enabled target distance evaluation without the need of a sonar’s ping, which could give away a submarine’s whereabouts.
Although the sinking of Japanese merchantmen was the US Submarine Force’s major contribution to the Pacific War, US submarines also accounted for the sinking of four Japanese carriers including Shinano (the world’s largest carrier, built on a keel laid for a sistership to the Yamato and sunk on her maiden voyage), Shokaku, Taiho and Unryu, as well as four escort carriers: Chuyo, Jinyo, Otaka, and Unyo. Submarines also sank a battleship (Kongo), along with four heavy cruisers (Atago, Kako, Mayo and Ashigara) nine light cruisers (Agano, Izuzu, Nagara, Natori, Oi, Tatsuta, Tenryu, Yubari and Tama) 38 destroyers and 23 submarines. Some US submarines achieved astonishing records; USS Flasher, a Gato Class submarine launched in June 1943, alone sank 100,231 tons of Japanese shipping while USS Tautog, a Tambor Class submarine that operated throughout the entirety of the Pacific War, sank a record 26 ships.
While economic strangulation of Japan became the key task of Submarine Force, on numbers of occasions US submarines also destroyed key Japanese personnel. On 8 May 1942 USS Grenadier (Tambor Class) sank the 14,500 ton Taiyo Maru off Kyushu killing hundreds of Japanese scientists and technicians heading south to take on the task of resource management in Japan’s newly acquired empire – particularly its oil assets. In April 1944, Japan’s bid to reinforce its defenses in western New Guinea was disrupted by the sinking of Yoshida Maru by USS Jack (Gato Class), which drowned an entire Japanese regiment on its way from China.
At the end of the war submarines also destroyed thousands of small craft. On a single patrol USS Blenny (Balao Class), under the command of Lieutenant-Commander W.H. Hazzard, sank 63 Japanese trawlers, sampans and other small craft by gunfire or with hand grenades. Many of the Blenny’s targets were sunk by surface attack using their 5-inch deck-gun that, along with up-rated machine guns, was a typical up-grade towards the end of the war. As carrier aircraft increasingly took up the task of destroying Japan’s remaining merchant fleet and bombing the mainland, submarines took up a new role of rescuing airmen. 380 airmen were rescued in 1945.
It was a record that did not receive due acknowledgement at the time. Inevitably security required that America’s submarine force was a silent service. The cost of not being silent became a stark reality when Kentucky Democrat Congressman Andrew May, after a briefing during a press junket to the war zone, revealed that Japanese destroyers were underestimating how deep US submarines could dive with the result that they were setting their depth charges too shallow. May revealed this information at a press conference, which immediately became public news, leading the Japanese submariners to reset their charges. An incredulous Lockwood wrote sarcastically to Admiral Edwards: “I hear… Congressman May… said the Jap depth charges… are not set deep enough… He would be pleased to know the Japs set’em deeper now.” After the war Lockwood estimated that the ‘indiscretion cost us ten submarines and 800 officers and men.”32
Indeed Japan’s later depth charges were increased to 147kg (from 100kg) of Type-97 explosive (70 percent TNA/30 percent HNDA) and a 300ft setting was introduced. When Japan introduced the Type-2 depth charge that carried 105kg, they significantly increased the weapons flexibility closer to British design, with detonation settings at 98 feet, 197 feet, 292 feet, 390 feet, and 480 feet. After the war Democrat Congressman Andrew Jackson May was convicted of bribery charges relating to payments for munitions contracts while he was Chairman of the House Military Affairs Committee during the war.
Fortunately for Lockwood’s Submarine Force, changes to Japan’s depth charges took place too late to have a significant impact on the war. In total just twenty-two US submarines were lost to depth charges. By comparison, depth charges accounted for eighty-five kills of Japanese submarines.