The JM cloche is an element of the Maginot Line. It is a non-retractable non-rotating cupola of steel alloy like GFM cloches, but are armed with twin heavy machine guns, as opposed to the lighter automatic rifles associated with the GFM. There are 179 JM cloches on the Maginot Line. JM is an acronym for Jumelage de Mitrailleuses(twin machine guns). While the Mle 1931 Reibel heavy machine guns were of the same caliber (7.5mm) as the GFM FM 24/29 guns, they had a longer practical range 1,200 metresand a maximum range of 4,900 metres, with a 450 round per minute rate of fire. The JM cloche closely resembles the GFM cloche in size and construction. It exists in three versions, all designed Model 1930: small, large and two-man. JM cloches had a single firing port, which was flanked on either side by trapezoidal observation ports. The blank rear was frequently backed by a concrete-covered embankment, which provided additional cover and reduced the prominence of the cloche.