To claim that the Japanese -- architects of the Bataan Death March -- were prosecuted for "waterboarding" would be like saying Ted Bundy was executed for engaging in sexual harassment.
What the Japanese did to their POWs made even the Nazis blanch. The Japanese routinely beheaded and bayoneted prisoners; forced prisoners to dig their own graves and then buried them alive; amputated prisoners' healthy arms and legs, one by one, for sport; force-fed prisoners dry rice and then filled their stomachs with water until their bowels exploded; and injected them with chemical weapons in order to observe, time and record their death throes before dumping them in mass graves.
While only 4 percent of British and American troops captured by German or Italian forces died in captivity, 27 percent of British and American POWs captured by the Japanese died in captivity. Japanese war crimes were so atrocious that even rape was treated as only a secondary war crime in the Tokyo trial, similar to what happens during an R. Kelly trial.
The Japanese "water cure" was to "waterboarding" as practiced at Guantanamo what rape at knifepoint is to calling your secretary "honey."
The Japanese version of "waterboarding" was to fill the prisoner's stomach with water until his stomach was distended -- and then pound on his stomach, causing the prisoner to vomit.
Or they would jam a stick into the prisoner's nose so he could breathe only through his mouth and then pour water in his mouth so he would choke to death.
Or they would "waterboard" the prisoner with saltwater, which would kill him.