Hi, for those of you who haven't already tried the Britain From Above website I can highly recommend it as a resource for some excellent views of various fully manned and armed fortifications. The archives aren't complete yet but I have already found images of coastal batteries at Tynemouth, Portsmouth and Isle of Wight dated 1937.
You need to register to the site to enable the Zoom facility (Its Free). The site also allows for groups of interest to be formed, so come on folks lets have enough people involved to start a fortifications group. Picture shows Old Bess, the 9.2" Mk X and one of the 6" guns at Tynemouth Castle battery dated 1937.