The distinctive helmet that Vic Morrow's Sgt. Saunders character wore in the series was covered with a piece of nylon cut from a U.S. paratrooper's camouflaged T-5 main parachute canopy, not a cloth Marine Corps cover as assumed by many viewers.
Several sources have stated that Rick Jason was to carry the M1928A1 Thompson submachine gun. After two days of filming, Jason complained about the weight of the Thompson and switched to the lighter M1 carbine and carried it throughout the rest of the series. Vic Morrow was then given the Thompson to carry. After two weeks, he also complained of its weight. A lighter replica Thompson was made out of wood and was carried by Morrow until it was time for a firefight, at which time he would switch back to the real Thompson. The replica can be seen with its incorrect ejection port. It should also be noted that officers usually carried a carbine and rarely a Thompson or M1 Garand.
According to the DVD box set, it cost Shecky Greene money to step away from his Las Vegas show to do an episode of this show. He left the series because of this.
Pierre Jalbert's character, "Caje", is supposed to be a Cajun (a group descended from the early French settlers of Louisiana who still speak French and keep to their own part of the state). Jalbert himself is actually a French-Canadian from Quebec.
Caje's full name and rank was Pfc. Paul Lemay, Kirby's was Pvt. William G. Kirby, Nelson's was Pvt. Billy Nelson. Littlejohn's first name was never given, and while Saunders on a few occasions was called "Chip" by soldiers who had known him in the past, including Lt. Hanley - who was in the same unit with him when both were NCOs - it was apparently a nickname and his real first name was never given.
Beginning with Vic Morrow and as the series progressed, the principal cast members were outfitted with expensive custom made fiberglass prop helmet shells to replace the heavier steel shell of the real two piece M1 helmets with which they began the series.