No disrespect intended, though it was controversial at the time. He was the specific target of operation Vengeance, and Frank Knox required FDR to sign-off on the Yamamoto assassination before he'd order admiral Nimitz to carry it out. When you specifically target an enemy leader outside of normal military operations it is generally called "assassination". The British used commandos to kidnap and/or kill German high ranking officers, so it's nothing unique.
