Yokohama Reviews - Asanobeating using hands, fists, club; kicking; water torture; burning using cigarettes; strapping on a stretcher head downward
On the solider in Viet Nam, I've found sites that said he was investigated and cleared, others say he was court martialed and discharged from the army. I haven't found any real info on that case, so it does not lend any credence to either side in my opinion.
On the Japanese war crimes, this guy says 7 were convicted and executed for rape, murder, massacre, and starving POW's to death.
Sorry, Paul Begala — You’re Still Wrong - By Mark Hemingway - The Corner - National Review Online
These 4 guys were also convicted of crimes including "water torture":
Yokohama Reviews - Sawamura
Yokohama Reviews - Minemo
Yokohama Reviews - Kita
Yokohama Reviews - Hata
It is also noteworthy that Japanese "water torture" appears to be materially different than waterboarding as used by the US recently:
Another description of Japanese "water torture":...forcing water down PWs throat and nostrils using among others a hose, tubes...
A type of funnel, usually formed from a towel, was placed over the victim's mouth and nose. At the same time, a 5-gallon can was filled with water and usually urine and kerosine. The concoction was poured into the funnel, and the victim had to either swallow all 5 gallons of this mixture or drown.
Having swallowed 5 gallons of this liquid, the victim's stomach would stretch and swell. The victim would then be bound, often with barbed wire, and the stomach would be struck, either with a rod of some sort or soldiers would even jump on it, depending on how the prisoner was bound. This pressure could easily cause the bloated stomach to burst. If not, the victim was then hanged by his ankles and the liquid would drain out through his mouth, risking drowning once again. The process could then be repeated.