Mines

Coupled with the Philippine campaign, the South China Sea raid effectively cut Japan from its possessions in Southeast Asia. To complete the isolation of the empire and to dismember the home islands, the Allies turned to a massive mining campaign bluntly named Operation Starvation. B-29 bombers from the U.S. Army Air Force’s XXI Bomber Command were tasked to drop naval mines into the harbors, inlets, and straights which connected the Japanese islands to each other and the rest of Asia. Japan had historically underinvested in its terrestrial transportation networks due to the cost advantages of maritime transport. As a result, local maritime shipping accounted for 2/3rds of material distribution between the home islands. A mine blockade afforded the Allies an opportunity to separate the Japanese empire from its remaining possession and from itself.From 1 May to 14 Aug 1945 the U.S. Army Airforce Force dropped approximately 12,000 mines, which took little over 5% of the command’s total effort. Most mining activity and the overwhelming density of sinkings occurred within the Kanmon straits, a critical waterway which connected the southern Japanese islands of Kyushu, Honshu, and Shikoku to the Korean peninsula and northern China. Merchant vessel sinkings attributed to mines accounted for 48% of sunken merchant vessels and 52 % sunken merchant tonnage. The pervasiveness of the minefields meant that they consistently claimed larger vessels than those destroyed by either subs or aircraft. The average vessel sunk by a mine during this period weighed over 2300 tons, whereas those sunk by aircraft and submarines averaged in at 1,910 and 2,067 tons, respectively.

Operation Starvation was the final significant Allied action aimed at statistically isolating the Japanese empire. It effectively cut off the Japanese home islands and accelerated the end of the war by consistently sinking the vestiges of the merchant fleet. U.S. Army Air Force mines sunk larger vessels than either air power or submarines and did so more consistently in the final months of the war. The 18,765 ton Kotobuki Maru was removed from this representation for scaling purposes.

Operation Starvation relegated conventional airpower to a supporting role. The last large U.S. air raid to yield significant merchant losses occurred on the Japanese island of Kure between 14 and 15 July 1945, during which U.S. naval carrier-based aircraft destroyed over 70,000 tons of merchant shipping. Supremacy of the mining effort also left few targets for Allied submarines in the final days of the war. U.S. submarines sunk a mere confirmed 11 vessels between 16 July and 13 Aug 1945 16 , on which date the USS Torsk (SS-423) sunk the Kaiho Maru , the last merchant vessel destroyed by an Allied submarine during World War II. 14 August 1945, the day of Emperor Hirohito’s “Jewel Broadcast,” U.S. Army Air Force mines destroyed three merchant vessels, the final merchant ships lost to enemy action during the Second World War.