Comments by "Sar Jim" (@sarjim4381) on "The Drydock - Episode 132" video.

Japanese subs sank about 75% of all merchant ships sailing from the west coast in the first month of the war. Her subs were the largest and fastest in the world in January, 1942, had the longest range of any sub, and had the most reliable torpedo with the largest warheads of any navy at the same date. Japanese sub skippers were more than willing to go after merchant ships. It was only orders from Tokyo that changed the targets to prefer warships. Captains that sank the most warships were also the most liberally rewarded by the Admiralty with promotions, so it didn't take long for sub commanders to fall into line. The USN would have had to devote many more resources to antisubmarine warfare, and supplies to the South Pacific would have taken much longer to arrive. While it wouldn't have changed the overall outcome of the war, it was a real missed opportunity on the part of the IJN to cause some real havoc here.
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@CSSVirginia Yes, it was the biggest single factor in their naval thinking. The writings of Alfred Mahan and the outcome of the Battle of Tsushima were the two stepping stones to developing the Kantai Kessen Doctrine (literally, "naval fleet decisive battle") that helped to seal the fate of Japan before the first bomb was dropped at Pearl Harbor.
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@spikespa5208 I'll need to go back and look it up again, but I'm fairly certain it was "The Japanese Submarine Force and World War II". The actual details of the sinkings came from a Hyperwar document, and I need to go back and dig that one out as well. You can probably find it faster if you search for Japanese submarine sinkings at Hyperwar.
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@John-ru5ud The IJN had a run of incredible luck plus good torpedoes for those sinkings. It was also before the USN had improved their ASW capabilities, making it nearly impossible to get close enough to a US task force for a repeat of those attacks. As we saw with the sinking of Indianapolis however, Japanese subs and unescorted ships were a fatal combination for the USN right up until the end of the war.
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