Complex sentence: In March 1951, the 3rd, 5th, and 8th Companies sailed for Korea, a trip which was fraught with frequent discipline problems as the Rangers continuously got into fights with US Marines onboard the troopship while "en route".
Split into simpler sentences: In March 1951, the 3rd, 5th, and 8th Companies sailed for Korea. The companies were known to frequently get into fights with US Marines onboard the troopship while "en route".