Early in 1937 it was recognised within the Bank that war with Germany was almost certainly inevitable. In February of that year the Treasury questioned the Bank about various measures that would be necessary before its outbreak, and much work was done to summarise and evaluate the steps which had been taken in 1914 and the later years of the First World War. From this period onwards the Bank was engaged in continuous preparations for what was referred to as ‘Zero’: preparations which were so thorough and complete in almost every respect that when war was finally declared on 3 September 1939 all the various activities of the Bank were able to continue with a minimum of interruption.

Air raid precautions, or ARP, had been instituted in Threadneedle Street in the autumn of 1914, but happily the Bank had been spared any direct hit from a bomb during the first war and no civilian member of staff received any injury from bombs while on duty. It was clear, however, that the danger from air raids was likely to be very much greater in any future conflict and, acting on the advice of the Home Office, the Bank began to consider the question of ARP in the spring of 1937. The two floors of enormously substantial vaults were regarded as offering excellent safety to members of staff even during the daylight raids on London which were anticipated, and arrangements were made for people to move underground if necessary.