Appendices - Hirohito's War
APPENDIX A: SUBMARINES - THE UNDERSEA WAR
Wasteful Dissipation of Japanese Submarine Force: Apart from the inefficient and bewildering profusion of weaponry in a force that boasted some thirty-nine different submarine types, Japanese submarine efficacy was blunted by the limitations put on their usage. At the outset of the war Admiral Yamamoto used his submarine force as an adjunct to the surface fleet. For the Japanese Navy, the submarine was primarily a fleet combat weapon rather than an offensive weapon aimed at disrupting the enemies’ commercial and economic strength. As naval historians Peatie and Evans have pointed out, the main conclusions drawn pre-war about submarines was their “vulnerability to detection by radio direction finding.”9 Unlike Germany the Japanese Navy did not use their submarines in wolf packs. Uniquely among the four major naval powers in World War II, Japanese submarines were commanded from shore; sea based command and control capabilities or tactics demanded by wolf pack operation were never developed. Although the Imperial Japanese Navy did recognize the possibility of commercial disruption, operational procedure emphasized the primary role of destroying enemy warships.
During the Pearl Harbor raid in December 1941 some 26 submarines were picketed around Hawaii with the aim of attacking any US ships that managed to escape the US fleet main harbor. In essence the Imperial Japanese Navy regarded the primary function of submarines as attack vessels in major fleet actions. As with the design of all of their fleet vessels, Japanese submarine design was predicated on the fighting of a single decisive fleet action.
Tactically, Japan’s Navy never acquired the correct balance between the need for stealth and attack. The emphasis was put on concealment and the patient waiting for the passing of capital ships before an attack was made from close quarters. Unlike the general preference of the Japanese Navy for attacking from long range, which the design of the Type-93 torpedo made possible, their submarine tactics advocated the principle of the sure-shot rather than firing from distance and escaping. After the war US Naval interrogators were astounded at the timidity of Japanese submarine tactics from a nation of the Banzai warrior: “It was frankly impossible to believe that [Japanese] submarines could spend weeks on the US west coast ‘without contacts’” one analysis recorded caustically, “or spend more than forty days among the Solomons during the Guadalcanal campaign without seeing any targets.”10 Given the exceptional courage of Japan’s military personnel, it seems likely that this overly cautious approach came from high command. Submarine expert, Norman Friedman, has stated that “The trade-off between preservation and combat effectiveness is central to submarine tactics and submarine design.”11 It seems that the Japanese Navy, in spite of its highly advanced torpedo and submarine design, failed to capitalize on these precious military assets.
Even the use of Japanese submarines as offensive assets against American capital ships changed after the Japanese reverse suffered at the Battle of Midway. Although the Kaidai Class I-168 finished off the badly damaged USS Yorktown after the battle and later in the year the USS Wasp, another fleet carrier, was sunk by B-1 Type I-19, this was the apogee of their success. As US carriers began to dominate the Pacific seaways, Japanese submarines were increasingly used as cargo carriers or troop transports. At the Battle of Guadalcanal, as the six-month engagement increasingly handed air supremacy to America, Japanese commanders increasingly resorted to using their submarines to supply or reinforce their troops stranded on the island.
Supply by submarine was hardly efficient. At Guadalcanal one of the larger submarines could carry only enough food to supply its Japanese forces for two days. By the time that the Guadalcanal conflict had ended, Japanese submarines had made 28 runs carrying an aggregate of 1,500 tons of supplies and munitions. To save space on the missions, crews were put on half rations. Two submarines were sunk. Up to September 1943 Japanese submarines also made 95 supply round trips from the southern HQ at Rabaul on New Britain to New Guinea. Just one submarine was lost in these operations. Not surprisingly Lieutenant Commander Zenji Orita protested: “using submarines for transport,” he complained, “is throwing away the reason for their construction.”12
When Japan’s main fleet was forced from Japan to Singapore in order to get closer to supplies of fuel, the Pacific was effectively surrendered to US control. When, after the Battle of the Bismarck Sea, air power started to shift even more rapidly toward the US, surface supply to New Guinea and Japan’s Pacific Island Empire became increasingly difficult. Not only supplies but whole regiments were lost as they transferred from China. Submarines increasingly became the only reliable way to sustain their military outposts. However, being reduced to missions as underwater supply and troop carriers was not conducive to fostering good morale in the submarine service. As Commander Nambu observed, “Subs were not meant be deployed as cargo carriers. Subs were meant to attack.”13
Even as supply vessels, submarines however were fighting a losing battle. US destroyers were not only increasing in numbers but by 1943 were receiving upgraded sonar equipment. Also the development of the Hedgehog, a forward throwing multiple mortar system, by the British Navy, which were adopted by the US as the Mousetrap proved even more effective than depth charges at killing submarines. (The Hedgehog took its name from the multiple spike spigots from which the mortar rounds were discharged). Forward throwing devices obviated the blind spot that destroyers had when they passed over a target before dropping depth charges from their rear racks. Japanese submarines were further disadvantaged by their size, their relatively slow submerging rate, and their lack of maneuverability.
In addition, the hulls of Japanese submarines were weaker than their American or German U-Boat counterparts. The thickly plated pressurized hull of a VII Type U-Boat would not rupture unless a lucky shot detonated within 4.6m. (In April 1945 the German U-427 survived 678 depth charges over many hours under attack). By contrast the US Mark 9 Depth Charge, introduced at the beginning of 1943 was devastating over much greater distances to the larger, less strongly hulled Japanese submarines which often provided a target double the size of a U-boat.
Knowing how deep to dive with the aim of avoiding destroyer depth charges was an unpredictable game of chance. Dive deep and a submarine was less likely to be hit. However the kill radius of a depth charge increased with depth because of the higher hydrostatic loading on hulls at lower depths. At near crush depth, any external detonation shock was more likely to cause catastrophic failure to the integrity of a submarine’s hull. By calculating the interval between the detonation bang of a depth charge and the powerful boom that followed, an experienced submariner might be able to calculate the depth, direction and distance of a depth charge and use the information to escape further attacks. However the most important requisite of a submarine commander was indubitably good luck.
As ground to air communication improved US carrier planes were able to join forces with destroyers; these tag tactics made search and destroy missions particularly successful. By 1944, with MAGIC intercepts also giving advance intelligence on submarine movements, the advantage in the undersea war had swung dramatically toward the US.
Built primarily as attack weapons, Japanese submarines’ design deficiencies became increasingly evident as the naval war turned in America’s favor. Large submarines were easier to sight visually. They were also slow diving, slow maneuvering, easy to track on sonar and were lacking modern radar of their own; their first sets were installed as late as June 1944 and were never comparable in quality to British and American technology. Lieutenant Commander Zenji Orita complained to Admiral Mito that “our chief weapon for detecting the enemy at present is 120mm binoculars. Top priority must be given to equipping First Class submarines with radar and electronic countermeasure devices.”14