For a very short movie, "Prison Ship", is surprisingly entertaining and tragically oh so believable.
The premise of the movie is based on fact. Japanese ships transporting prisoners-of-war during World War 2 did indeed offer themselves up as decoy targets, hoping to draw the US submarines away from their desired cargo ships and warships.
From that point the movie becomes a feel good exercise for an American audience, that by 1945 had cultivated a deep loathing for their enemy, and wished to see their own servicemen triumph against any and all impossible odds.
By 1945 Richard Loo was able to play his role blindfolded. Between late 1941 through to 1945 he was in 34 movies, invariably as the bad guy. In this movie Loo was the standout, the rest of the cast were merely competent.
If you have a spare hour, have a look, it's worthwhile for a fan of the genre.