During some of these nighttime attacks, PT boat positions may have been given away by a flash of light caused by grease inside the black powder-actuated Mark 8 torpedo tubes catching fire during the launching sequence. In order to evade return fire from the enemy ships, the PT boat could deploy a smoke screen using stern-mounted generators. Starting in mid-1943, the old Mark 18 torpedo tubes and Mark 8 torpedoes were replaced. The new Mark 1 "roll-off" torpedo launcher rack (loaded with an improved Mark 13 aerial torpedo) effectively eliminated the telltale flash of light from burning grease, did not use any form of explosive to launch the torpedo, and weighed about less than the tubes.