Opening with the Allied invasion of Normandy on 6 June 1944, members of the 2nd Ranger Battalion under Cpt. Miller fight ashore to secure a beachhead. Amidst the fighting, two brothers are killed in action. Earlier in New Guinea, a third brother is KIA. Their mother, Mrs. Ryan, is to receive all three of the grave telegrams on the same day. The United States Army Chief of Staff, George C. Marshall, is given an opportunity to alleviate some of her grief when he learns of a fourth brother, Private James Ryan, and decides to send out 8 men (Cpt. Miller and select members from 2nd Rangers) to find him and bring him back home to his mother.

Marine Heavy Gunner: Vietnam is a budget-priced first-person shooter that combines the seamless narrative style of Half-Life, the computer-controlled squadmates of Vietcong, the fixed-position gunplay of Beachhead, and Max Payne's over-the-top tough-guy dialogue. It's also filled with overheated, deranged metaphors, such as "Half of these jokers were doing the backstroke six feet under and had no idea, trying out for the swim team of the soon to be dead." That all might sound great, but unfortunately, Marine Heavy Gunner's actual execution leaves a lot to be desired. For what it's worth, though, the game does feature a really impressive amount of heavy-duty swearing.

Gameplay is split into three basic types. There are extended on-rail sections in which you man a gun mounted on various vehicles such as a helicopter, an armored personnel carrier, and a boat. These sections have neither the breakneck urgency nor the cool scripted set pieces seen in the best examples of on-rail levels from games such as Call of Duty or the Medal of Honor series. Like pretty much everything in Marine Heavy Gunner, they're functional at best.