The GFM cloche was one of the most common defensive armaments on the Maginot Line. A cloche (bell) was a fixed and non-retractable firing position made of a thick iron casting which shielded its occupant. By comparison, turrets could be rotated and sometimes lowered so that only the top shell was exposed.

GFM is an acronym for Guetteur et Fusil-Mitrailleur (lookout and rifle-machine-gunner), which describes its purpose as a lookout and firing position for light weapons. Most of the bunkers or blocks in a Maginot Line ouvrage were fitted with several fixed armoured cupolas or cloches. The cupolas were designed to allow the soldiers to perform reconnaissance or repel an attack with an absolute maximum of cover, from inside the bunker. The armament of each cloche varied significantly, but were typically equipped with some combination of:

• Light machine guns or automatic rifles
• Vision blocks
• Mounted binoculars
• A periscope (located on the top of the bell)
• A 50 mm mortar