Cloches and Cupolas were built into fortifications, such as the Maginot Line and Eben Emael, by European counties after WWI. The Cloche and Cupola models are typical of these defences. MG cloches were also built into sections of the D-Day Atlantic Wall.
Cloche (which is French for ‘bell’) was the the name adopted for armoured fortifications that were (generically) bell shaped. This type of fortification was typically used for observation posts and machine gun positions.
Cupola was the term adopted for armoured defences containing large calibre guns and were generally, dome topped artillery positions. The purpose of the cupola varied from the traditional artillery role (the surface mounted cupola), to close fire support (the retractable cupola). This is due to the retractable cupola’s ability to depress the elevation of the guns to the horizontal, combined with its ability to also fire canister rounds.