Complex sentence: Cliffe Fort saw about 60 years of usage as an artillery fort, from its completion in 1870 to its disarmament in 1927, but it saw service again during World War II to serve as an anti-aircraft battery on the approaches to London.
Split into simpler sentences: Cliffe Fort saw about 60 years of usage as an artillery fort, from its completion in 1870 to its disarmament in 1927. It was repurposed during World War II to serve as an anti-aircraft battery on the approaches to London.