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.
Vic Morrow and Rick Jason were essentially co-stars, and for this reason there were two sets of opening credits, some listing Morrow as the lead before Jason, and some listing Jason ahead of Morrow, although not necessarily based on which one had a larger role in a given episode.
Although Pierre Jalbert had been employed at MGM for nearly a decade, he had no actual acting experience prior to being cast as Pfc. Paul "Caje" Lemay on the series. Up to that time his job at MGM had been in the capacity of a technician in the film editing department.
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.
The distinctive helmet that Sgt. Saunders (Vic Morrow) 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.
Sgt. Saunders was referred to as "Chip" several times over the course of the series. While "Chip" is a common nickname for Charles, he is never referred to as Charles, Chuck or Charlie. Lt. Hanley is addressed as "Gil" in the first episode of the series. "Gil" is usually short for Gilbert, but other than that one time, Hanley's actual first name is never mentioned again.
Caje's full name and rank was Pfc. Paul Lemay, Kirby's was Pvt. William G. Kirby, and Nelson's was Pvt. William 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 they were NCOs, it was apparently a nickname, and his real first name was never given. In Season 1, Episode 11, "A Day in June", the D-Day invasion was told in flashback. Then-Sgt, Hanley is addressed by a young lady, with whom he was keeping company, as "Gil" when the men are ordered back to their posts.
Comedian Charlie Callas was a big fan of the series and asked Rick Jason (I) if he could have the M1 carbine Jason's "Lt. Hanley" character carried on the show after it ended. Jason had the gun's barrel plugged and gave it to Callas, who mounted it over the bar in his house. Since Callas' passing, the whereabouts of the weapon is unknown.
The M-1 carbines carried by Lt. Hanley and various other characters have a prominent bayonet lug on the bottom of the barrel, marking them as the later Korean War variant of the weapon. The M-1 carbines issued in World War II were not equipped to mount a bayonet.
The series lasted five years in spite of the fact that only eleven months elapsed between D-Day on June 6, 1944 and the German surrender on May 8, 1945. However, the episode count (152) was less than half the number of days (336) between the two events.
During the entire series, Sgt Saunders was wounded about 46 times during the series. Apart from earning scores of Purple Hearts, his recovery time for each gunshot or explosion wound would've kept him in the hospital for weeks and months and, in reality, he would've spent more time in a hospital bed than seeing action, that is if he were returned to duty at all and not sent back to the states with a medical discharge.
The trivia items below may give away important plot points.
In one episode, a railcar is shown with a particular coded nomenclature that shows a date of 06-08-58, a full 13 years after the end of WWII. In other episodes, other railcars are shown without the European car coupling bumpers but instead, only the typical North American coupling device.
In Season 1, Episode 15, "Just for the Tecord", Saunders is called "Chip" by his mother in a phonographic recording sent to him by his mother and his sister. It is also revealed by Saunders in this episode that he is from Cleveland, OH.
In Season 1 Episode 1, it can be seen on Caje's left arm (visible on the far right of the screen) you will see that they are, (at least he is) apart of the seventh army, a division which served from 1943 - 1945, later re-established 1950 - Present.