The plot is based around a Motor torpedo boat and crew during WW2 filmed on a real boat with as I understand it the real crew in 1945.
The storie follows the crew and boat on several uneventfull trips, and shows the crew on board and in the pub and quarters They finally encounter the enemy is the last part of the film.
Its worth a watch to see the real wartime craft and uniforms and how the crew interact. I actually really enjoyed it.