Firefighters were called out just before 5 pm to Battery Moltke at Les Landes to find the man lying on the stairs inside with suspected spinal injuries.
Crews had to use specialist hydraulic equipment to lift the door and get him onto a stretcher and out safely before he was taken off to hospital.
The man, one of the volunteers who helps maintain the Island’s German bunkers and shows people around them, is still in hospital this morning but is said to be in a comfortable position.
Police say it looks likely one of the bunker’s hatches hadn’t closed properly.
(Picture credit: Jersey Fire & Rescue)