In 1939, Britain entered the Second World War, and a number of the school's teachers were called up to fight in the British Army. Headmaster McGregor Williams meanwhile joined the Home Guard, eventually becoming the head of the Chislehurst platoon. At the school, the students set about digging out trenches to use as bomb shelters and assemblies were cancelled. Students were expected to carry their gas masks around with them in case of chemical attack, and during the ensuing Blitz – in which the German Luftwaffe began bombing London and the areas around it – the school was affected by a nearby landmine on 17 September 1940, destroying the glass of all the windows on one side. On 16 June 1944, the school was once more struck, this time by a V-1 flying bomb which destroyed one end of the Assembly Hall; much of the damage to the school would not be permanently repaired until 1951. By the time that the war came to an end in 1945, 280 former pupils and 13 members of staff had fought in the armed forces, with 45 of them having been killed.