(CNN) - Sen. John McCain said Monday he was "disappointed" that some candidates vying for the GOP presidential nomination vocally support waterboarding as a technique for interrogating suspected terrorists.
"Ask any military lawyer, ask any person who knows about the Geneva conventions that we're signatories to. We actually prosecuted Japanese war criminals specifically for the act of waterboarding against Americans," McCain said on CNN's "John King, USA."
The Arizona lawmaker was reacting specifically to comments made by Texas Gov. Rick Perry, former pizza executive Herman Cain, and Minnesota Rep. Michele Bachman at Saturday's GOP presidential debate.
McCain said Monday that waterboarding was not only illegal, but ineffective.
"If you put enough physical pain on somebody, they will tell you whatever they think that you want to hear in order for the pain to stop," McCain said.
McCain said the person elected president needed to display leadership to ensure Americans know international law prohibits torture.
"It's a matter of the president telling the American people about the Geneva Conventions," McCain said. "And why we didn't torture prisoners in World War II. That was because they had Americans as prisoners. And why we prosecuted people for the very same act of waterboarding after World War II was over."
McCain took a strong stance against waterboarding when he was running for president in 2008. A former naval aviator, McCain was shot down by the North Vietnamese in 1967, and endured years of imprisonment and torture as a POW.
At the debate Saturday night, hosted by CBS News and the National Journal, three candidates came out in support of waterboarding.
Perry defended the practice, saying: "This is war. That's what happens in war."
Cain said of waterboarding, ""I don't see that as torture. I see it as an enhanced interrogation technique."
Bachmann called the tactic "very effective" and said Obama "is allowing the ACLU to run the CIA."
Speaking to CNN's Wolf Blitzer Monday, former Pennsylvania Sen. Rick Santroum said he did support waterboarding, citing its role in locating terrorists.
"This is something we should not use cavalierly by any stretch of the imagination, but if absolutely necessary, for the security of our country, we have to have methods available to extract from people who are not protected by the Geneva Convention," Santorum said on "The Situation Room."
Other candidates, including former Utah Gov. Jon Huntsman and former Massachusetts Gov. Mitt Romney do not support the tactic.