On Ille Cézembre outside the city of St. Malo in Brittany the German navy started in 1942 construction of a gun battery with six French 194 mm. rail guns. These were placed in open ring positions and therefor had a 360° field of fire. The guns were from 1870 and for controlling the guns a large command bunker (M157) was built. The range of the guns was 15 km. and to protect the guns several anti-aircraft positions, ammunition and crew bunkers was spread around the island.
Cézembre was part of "Festung st. Malo ", but after the Americans in early August captured the city itself, the island was completely isolated. The garrison that consisted of nearly 500 German and Italian soldiers refused to surrender and the next week the island was turned into the most bombed area throughout World War II. Both from the the water from the land and from the air the island was bombed beyond recognition. The Germans tried to get supplies in from Jersey and several severely wounded to be returned, but the massive bombing eventually got the garrison to surrender. This takes place on September 2 and only after the water supply has run out.
Because of the massive bombing in August 1944, large parts of the island is still filled with unexploded shells, bombs, mines and bomb craters. Most of the island is fenced in and off limits.