From Halopedia, the Halo wiki
The Desert Eagle is a human semi-automatic handgun. Designed in the 20th century, they are considered antiquated by the 26th century. Some examples of the weapon still existed in museums, with one such example having been looted by Istvan Erdei. Despite its extreme age, the weapon was still functional, with Erdei confident it would be able to penetrate the helmet of John-117's GEN3 MJOLNIR armor.
The Desert Eagle is a real-world handgun, notable for its large ammunition.
List of appearances