December 28th - The Day of Infamy, Part XVII

The Silent Service

While Japanese forces fought in the Solomon Islands, others were fighting an increasingly desperate battle to keep them supplied. The improved performance of US torpedoes, coupled with slowly improving tactics and assignment of operational zones – hunting grounds, as the sub skippers called them – were making the US submarine force one of the most deadly weapons being wielded against Japan.

By the end of 1943 over a third of the Japanese pre-war merchant fleet had been sunk, the vast majority of the losses being inflicted by submarines. During 1943 Japanese merchant ships were being sunk ten times faster than they could be built. Dozens of destroyers, numerous lighter combatants, and several major combatants had been lost as well.

In November of 1943 Yamamoto recommended that construction on all ships larger than destroyers not at least 50% complete be suspended, work being shifted to escorts and merchant ships. Condemned by some as defeatist, this recommendation was supported at least in part by others, who noted that at the present rate the Japanese destroyer force would cease to exist by the end of 1945, despite new construction.

The reasons for Japan’s plight were many. Convoys had been slow to form and even at the end of 1943 many ships sailed alone. Escorts were scarce due to low pre-war priorities, and only so many destroyers could be withdrawn from Combined Fleet for escort work. The need for light forces to fight in the Solomons had further drained the escort pool. What escorts were available were poorly trained for ASW and equipment varied dramatically. In particular depth-charge patterns were usually set fairly shallow, meaning that a US submarine that managed to evade the initial attack was typically able to break contact without damage. This stood in sharp contrast to Allied ASW, who were able to prosecute-to-kill on a regular basis.

The US ability to mass-produce good fleet boats also played a key part. While Japan seldom built more than half a dozen boats to a single design, the US built over 30 Gato-class boats in 1942 and again in 1943, along with two dozen Balao-class boats that had only slight modification from the Gato-class. This standardization was a tremendous benefit in training crews and applying tactical lessons.

The vaunted U-boats loudly threatened Britain. The Gatos silently strangled Japan.