看imdb上的簡介:

During World War II, an American destroyer meets a German U-Boat. Both captains are good ones, and the engagement lasts for a considerable time.

好像是the enemy below沒錯
假如影片中有一段德軍在潛艇中
大唱軍歌來激勵士氣的片段就更
能確定是這一片
雖然是老片，可是很好看！