content: Black smoke were smoke dischargers, basically a smoke grenade launcher, white smoke was from smoke generators, an oil mixture is vaporized and mixed into the exhaust stream from the engine. The intent is to screen the landing infantry force against directed weapons fire (small arms, machine gun emplacements, tank guns, etc). The landing vehicles go in waves and put out the smoke as defense for next landing wave. With proper wind conditions then the smoke will last for quite a while instead of blowing away or dissipating too quickly, though it is obviously far less effective in the open than it is in more urban conditions.