after WWII, Japanese soldiers who'd waterboarded their American prisoners were put to death by the US military for committing unconscionable acts of torture.

I can't seem to come up with any reliable account of these excecuted Japanese soldiers online. Can you cite your source?

From what I can find, it appears the U.S. only prosecuted one Japanese officer for the practice (along with charges of other torture methods), and he received a prison sentence.