The Technical Intelligence Section within the Research and Experiments Branch grew into the Technical Intelligence Division (B Division) as a result of the expansion of its bomb census field organisation.
The study of the effects of air raids assumed new importance in August 1940, when it was seen that it might throw light on the technique of enemy attack. After consultation with the Air Ministry, the field organisation undertook to collect information bearing upon the type, weight and distribution of bombs, the mean point of impact of groups of bombs, the time of attack and fall of each bomb, the duration and phases of attack, the type of aircraft, height of aircraft, direction of attack, use of flares, weather conditions and other circumstances. The enterprise became known as the Bomb Census, and from September 1940 it operated on a limited basis in London, Birmingham and Liverpool.
In March 1941 the Air Ministry made it known that more detailed and accurate information was required to take account of variations in German bombing techniques, and thereafter particular incidents were investigated more thoroughly and the census extended. By September 1941 the field organisation was operating throughout all the civil defence regions, with the exception of the Isle of Wight, the Scilly Isles and the Isle of Man. As air attack was liable to be intermittent and scattered and in order to avoid a large full-time staff waiting to investigate attacks at any point, use was made of organisations able to co-operate locally with the census, including the police and civil defence services. To co-ordinate this local assistance, train the staff of the co-operating authorities and help in the plotting of bombs in special circumstances, area technical officers were appointed, each dealing with a county or other suitable unit and working under the appropriate regional technical intelligence officer.
As the research work of the Research and Experiments Department expanded, the scope of the technical work of the field organisation widened in consequence, and a considerable amount of data was furnished in connection with shelter construction, factory protection, building design and civil fires. The headquarters staff at Princes Risborough was organised into a Bomb Census and Operations Group, Technical Group and Training Group, reflecting the three main aspects of the administration of the field staff.
In March 1942 some of the analytical work of the division was allocated to appropriate research sections, and a Technical Intelligence Committee was established to preserve the close relationship between analysis and collection which had existed prior to the reorganisation. It also undertook the issue of instructions to the staff of the field organisation.
In January 1943 the Air Ministry took over the investigation of both high explosive and incendiary attacks on main target towns and selected targets in open country, while the Ministry of Home Security remained responsible for the collection of routine information in all other areas. From November 1940 to January 1943 B Division summarised the census information weekly, and thereafter monthly. The division also collected and circulated information such as the details of bomb construction, the resistance of different types of building and the efficacy of fire-fighting methods.