Who (name and rank) was the highest ranking U.S POW in history?

I was watching a movie, which was supposed to be based on fact, (Vietnam era) and one of the POW's was a rear admiral. Not sure if he was a US officer, but most of the other POWs were US officers. I was somewhat shocked, since I thought that in modern warfare such high ranking officers are far from the action. A navy Rear Admiral is like an army Brig. General, is he not? Any thoughts?