Hello. We bought a 1937 semi in Sheffield a couple of years ago with a pretty good size bunker under the middle of the back garden with a thick concrete roof. We are maybe 1/2 a mile south of steelworks at Stocksbridge. Is it conceivable there could have been an anti-aircraft gun at the end of our garden and ammunition would have been kept in the bunker? This is what the previous owner led us to believe. Also, can somebody identify this and how do I know if it's safe?