Complex sentence: The production of the first British-made Oerlikon guns started in Ruislip, London, at the end of 1940; and the first guns were delivered to the Royal Navy in March or April, 1941.
Split into simpler sentences: The production of the first British-made Oerlikon guns started in Ruislip, London, at the end of 1940. The first guns were delivered to the Royal Navy in March or April, 1941.