Abstract To drill boreholes for water supply, the Royal Engineers raised ten ‘Boring Sections’ between September 1939 and May 1943, eight in the UK, two in Egypt. While supporting campaigns in World War II, two deployed briefly to France, seven served widely within the Middle East (one of these in Iraq and Iran and later Malta, the others mostly operating from Egypt), one deployed to Algeria/Tunisia, four to Sicily and/or Italy (one of these onward to Greece), two deployed to support the D-Day Allied landings in Normandy and the subsequent advance via Belgium to Germany, and three served long-term in the UK. Greatest use was by Middle East Command, which at its peak had about 35 officers, 750 men and 40 drilling rigs assigned to water supply, and whose boreholes attained a cumulative length of some 40 km. The British Army used geology to help guide emplacement of boreholes in all these regions. Innovations included groundwater prospect maps at scales of 1:50 000 and 1:250 000, to help planning for the Allied invasion of Normandy and the subsequent campaign in NW Europe. Geology also helped guide groundwater abstraction by Indian Engineers in the Far East, and British/South African troops in East Africa.