Cigarettes were given to the soldiers free of charge and everyone smokes to kill the time, but smoking up on deck could get everyone killed. If a U-boat sees the flame your ship could be torpedoed. Even smoking below deck could start a fire.

Even though the urge to light up was very strong you resisted. There will be plenty of time in daylight to have a puff. A few minutes later you heard that the RPs caught a smoker on deck. He'll be spending the rest of the voyage scraping and painting and an ocean liner as a lot of surface that needs repainting!