How Allied Submarines Crippled Japan in WW2

This paragraph discusses the pivotal role of the Battle of the Atlantic during World War 2 and contrasts it with the lesser-known U.S. Navy's campaign against Japanese merchant shipping in the Pacific. Initially, the U.S. Navy did not plan to use submarines as a primary weapon against Japanese shipping, and even advocated for a ban on submarines in the 1930s. However, as war with Japan became imminent, submarine construction was accelerated. The U.S. submarines, like the Gato and Balao classes, were designed as 'fleet' submarines, larger and with greater capabilities than their German counterparts, intended for attacking enemy warships rather than merchant ships. The attack on Pearl Harbor led to a change in strategy, with Admiral Harold Stark ordering unrestricted warfare against Japan. Japan's war economy was highly dependent on shipping, making it a prime target for the U.S. Navy. Despite the initial lack of focus on merchant ships, U.S. submarines managed to sink a significant number of Japanese merchant vessels in 1942, although the actual numbers were later revised downward in post-war assessments.

The second paragraph delves into the challenges faced by the U.S. submarine fleet during World War 2 and the subsequent improvements made. The Mark 14 torpedo, the standard weapon for American submarines, was found to be unreliable, with numerous reports of failures to explode. This was exemplified by the USS Sargo's unsuccessful attempts to hit targets. The torpedo had issues with both contact and magnetic detonation methods, which the navy was slow to acknowledge and address. Additionally, there were concerns about the submarine officers' aggressiveness and the lack of a coherent strategy from the top brass. Historian Clay Blair criticized the navy's approach, suggesting that submarines should have been focused on interdicting Japanese merchant shipping. Rear Admiral Charles Lockwood, who took command in 1943, redirected more patrols to the key area north-west of the Philippines, which resulted in a significant increase in sinkings. The year 1943 saw an improvement in the submarine fleet's performance, with more ships sunk and better availability of torpedoes, although the Mark 14's reliability was still an issue. The Japanese, recognizing the threat, established the 'Merchant Escort Command' under Admiral Koshiro Oikawa to protect their merchant shipping.

The final paragraph outlines the dramatic impact of U.S. submarine operations on Japan's war economy in 1944 and beyond. By the start of 1944, U.S. Pacific submarines had become highly efficient, with improved crew coordination, 'Wolfpack' tactics, superior radar technology, and valuable intelligence from ULTRA decrypts. They achieved significant success against Japanese warships, sinking numerous vessels including battleships and aircraft carriers. The capture of the Mariana Islands provided a strategic base closer to Japan's shipping lanes, which significantly increased the pressure on Japanese merchant shipping. The loss of merchant ships reached unprecedented levels, with 548 sunk by submarines alone in 1944. The recapture of the Philippines further isolated Japan, severely disrupting its oil supply and leading to a collapse in imports and the size of its merchant fleet. The effects on Japan's war economy were catastrophic, with critical shortages of fuel and raw materials, ultimately leading to a halt in production and the strangulation of its ability to move goods within its empire. The success of the submarine campaign was a key factor in the defeat of Japan, despite being one of the least known battles of World War 2.