This question arises from me doing some research for fact-checking some things Noam Chomsky said about Nuremberg, specifically in this comment I wrote that got a bit buried in a bigger thread.
Specifically around Karl Dönitz's trial and the charges he faced. Specifically it looks like he was charged (and found guilty, but not sentenced) for having U-Boats attack neutral merchant ships in Atlantic war zones. Supposedly part of why no sentence was passed was because of the mitigating factor of the Allies doing something similar.
It made me think about the US submarine campaign against Japan. One of the justifications the US provided was that it was attacking Japanese merchant ships, which were effectively (in the US argument) auxiliaries of the Imperial Japanese Navy. Dönitz was actually acquitted of a similar charge (attacking British merchant ships). But his conviction for attacking neutral ships made me wonder: did US submarines sink any neutral shipping off Japanese waters? Was there any neutral shipping? US Navy records only seem to record Japanese sinkings, such as here. But were any other countries' ships sunk? I'm trying to think who else would even send ships to Japan in 1941-1945, besides maybe the USSR, Portugal (with Macau) and possibly occasional neutral ships for diplomats.
Curious if anyone has any info on this.
I was going to point to this article, which details the sinking of six Soviet flagged merchant ships by US submarines and was posted in another thread. Then I realized you are the one who had posted it. The author states that, "As a rule, Soviet vessels underwent American torpedo attacks in bad visibility conditions: in fog or at night." Any sinking of a neutral ship would be a mistake, but doing so at night would have required a major mistake on someone's part, since Soviet ships should be sailing straight with lights on, something a Japanese ship would never do.
Portugal mainly seemed concerned with the safety of their cod fishing fleet on its journeys to the fishing grounds in the North Atlantic. Everything else in the Pacific was for the most part, shipping belonging to one of the combatant countries.
The greatest tragedies for the US submarine fleet in the Pacific didn't involve neutral ships, but rather the sinking of the Japanese transport ships, Montevideo Maru, Rakuyo Maru. and Kachidoki Maru. The Montevideo Maru was unescorted and unmarked near the northern Philippine coast when it was sunk by the USS Sturgeon on 1 July 1942. It contained 1054 Australian prisoners, mostly of the 2/22nd battalion and a number of civilians all of whom were captured at Rabaul. A number of Japanese crew survived, but all of the POWs were lost. The unmarked Rakuyo Maru and Kachidoki Maru were sunk on 12 September 1944 by the USS Sealion and two of its sister submarines in the Luzon strait. 1159 of the 1307 British, Australian and 1 US POW aboard the Rakuyo Maru were lost. An additional 431 POWs from the Kachidoki Maru were also lost. All of these were POWs being transported from Burma, most of whom had worked on the river Kwai bridge.