The series details his adventures and exploits as a U.S. GI, and former US Army Ranger, fighting in France during World War II.
Mahoney, with his always present side-kick, Corporal Edward Cranepool, become involved in several of the key battles for the liberation of France, and invasion of Germany.
Later, tired of always finding himself involved in "suicide" missions, Mahoney and Cranepool transfer to the "Hamerhead" Division in General George S Patton's 3rd Army.
In the first book in the series, Death Train, which takes place in the summer of 1944, Mahoney is a US Army Ranger working behind German lines with the French Resistance, "maquis", to disrupt a rail-road line that will be essential to German troop and supply movement after the D-Day invasion on Omaha Beach.
The book establishes Mahoney as a tough, career Army, individual, and an experienced combat veteran that had seen action since the initial US amphibious landings in 1942 at Morocco.
They used a uniform cover design featuring a large color, portrait drawing of a US GI (Mahoney), and a small combat action scene in the lower right.