Completed in 1942, the Stronghold was an underground broadcasting studio adjacent to Broadcasting House and facing onto Duchess Street. It provided a complete broadcastind studio in miniature, to be used in the evnt of Broadcasting House being rendered unusable by enemy bombing.
It was constructed using 10,000 tons of concrete and, despite some bomb damage to the above ground studios, was never used in anger. Although originally intended to be incorporated seamlessly into the (then) planned Broadcasting House extension, the eventual design of the extension when built in 1962 was at differenmt levels which led to some compromises.