I read in the synopsis that it takes place in 1918. However there a number of references in the reviews here that say it takes place during 'The London Blitz' (which took place from 1940-1941. Was it a Dirgiable that dropped the bombs in the film?
I take it you haven't seen "Return of the Vampire?"
Well the first part of the film takes place in 1918.
Then after Vampire, "Armand Tesla" is staked, the film moves to the present day of 1943 when this movie was filmed.
During the Blitz, the grave yard where Tesla was buried is hit with a bomb and several corpses are exposed.
Two workers that were re-covering the bodies, see Tesla with a stake in his heart and they pull it out, which causes Tesla to return to his vampire life.
It starts in 1918 and in one scene later in the film Lugosi says he was waiting for 23 years to come back, so that sets it in 1941 which would be during the Blitz.