[dragoon500ly]

In any discussion of WWII, the German U-Boat campaign seems get get the most attention. The U.S. slaughter of Japanese shipping is seldom mentioned. U.S. submarines accounted for over half of Japanese merchant shipping. The increasing reach of American land and carrier-based aviation complemented this effort, ensuring that Japanese shipping was under attack almost from the moment it left Japan until it arrived at their front line bases.

This shortfall of shipping was assisted by new construction, but at rates far less than that of the Allies, typically some 500,000 tons of new construction a year with a peak, in 1944 of 1.7 million tons (the same year that the US sank 2.7 million tons).

By the end of 1943, Japan's merchant marine was crippled.

Submarines accounted for 5,880,000 tons sunk during the war, roughly 62% of the total.

Carrier aircraft accounted for another 1,740,000 tons, 18% of the total.

Land based aircraft added 825,000 tons, 9% of the total sunk.

Mines accounted for 600,000 tons or 6%.

And finally 450,000 tons were sunk by accidents at sea or by surface ship action, some 5 % of the total.

Another way of looking at Japan's situation is this:

In Dec. 1941, 6.4 million tons were available.

In Jan. 1943, 5.9 million tons remained.

In Jan. 1944, 4.8 million tons remained.

In Jan. 1945, available shipping had been reduced to 2.4 million tons.

And in Aug. 1945, the Japanese merchant marine was reduced to 1.5 million tons.

USN submarines spent 31,671 days on patrol (roughly 3 weeks on patrol). In attacking 4,112 Japanese merchant ships, US subs expended 14,748 torpedoes (roughly 3.6 per attack). Because of defective torpedoes, the odds of sinking a vessel, from 1941-1943 was less than 20%. It rose to 50% for the rest of the war.

US Subs confirmed the sinking of 188 warships and 1,294 merchant men, this does not include ships attacked, damaged and later sank by some other means. This cost the USN 49 submarines.

The IJN lost 130 submarines in WWII; the British lost 3 subs and the Dutch lost 5 subs in the Pacific. Allied submarines sank 2% of all Japanese shipping sunk.

Japan started the war with 67 subs, the US Pacific Fleet had 56 subs. The IJN built 120 subs during the war....the US built 200.

As successful as US subs were, their crews took high losses. 22% of all US submarine crews were killed during the course of the war. This is the highest percentage loss of any arm of the service.