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Work has continued on the assessment of military sites of the twentieth-century for the MPP, undertaken by the CBA. The first phase of this project covering, five major classes of monument (anti-invasion measures 1939-45, anti-aircraft artillery 1914-46, bombing decoys 1939-45, Operation Diver sites 1944-45, and Operation Overlord preparatory sites 1942-45) is complete, and the project has continued to a second phase covering coast artillery 1900-56, civil defence 1939-45, acoustic detection and radar 1920-45, airfield defences 1940-45, and Cold War sites 1947-69. Following the pattern of previous work, the survey is national and based upon information held at the Public Record Office, Kew. Such documentary sources are preserved in staggering quantities, and range from the daily records of military units to paperwork deriving from civil service offices and government departments. Here the aim is to record sufficient information to provide an adequate assessment of twentieth-century military sites. As well as providing historic context, each report gives details on chronology, typology, and site location. Locational information is of particular interest, especially given our intention to guide the Defence of Britain Project in its field-recording programme. In all cases except civil defence and anti-invasion measures, the locational information will come close to providing a complete record, to the accuracy of a six figure grid reference (converted from the wartime Cassini grid).
The assessment of airfield defences is nearing completion. By early in 1945 Britain had 740 airfields, many of which were defended to some extent, those in place in the first three years of the war having the most substantial fabric. How many defence works were built cannot be stated precisely; we do know, however, that in the year from September 1940 the most heavily defended stations were each allotted between 20-32 pillboxes, together with around 10 dummy pillboxes; the most lightly defended stations were given 10-12 pillboxes and 6 dummies; and all received as many earthwork weapon pits as were considered necessary. In addition, the most vulnerable stations were provided with 2 or 3 specialised 'disappearing' pillboxes, known as the Pickett-Hamilton fort, a structure used only on airfields, and designed to rise up on pneumatic pressure from a sunken position. Some 335 of these were built in Britain; it is not yet known how many survive.
The survey has also provided information on the internal layout of airfields, reflecting the frequent adjustments to airfield defence policy as the war progressed. In the early summer of 1940 for instance, airfield ground defences consisted largely of conventional infantry weapon pits and improvised emplacements for Lewis guns, supplemented by sites for 40mm light anti-aircraft weapons. The second phase, in which the development of airfield defences ran in parallel with a national system of anti-invasion measures, began in June 1940. This episode is characterised chiefly by the introduction of pillboxes, but in numbers governed by no generally defined plan. The beginning of the third phase is marked by the issue of the Taylor Report in late September 1940 when, for the first time, airfield defences were conceived as part of a national scheme and definite scales of weapons, troops, and defence works were laid down. The fourth phase is the least distinct, and embraces a host of changes and adjustments visible from the autumn of 1941. The abandonment of pillboxes is one of its chief characteristics, together with the introduction of several new structures on a national scale, most notably the Air Ministry battle headquarters and the spigot mortar, a new anti-tank and anti-personnel weapon of which 28,000 had been issued by late summer of 1942. This phase saw the gradual outward extension of airfield defences and a move away from static layouts and tactics in vogue during the summer of 1940. The final phase, active from the summer of 1942, saw still further expansion into site hinterlands.
These five phases provide a distinct chronology of change and development. Of course, any one airfield may contain traces of several different phases of works, depending on when the station was built. Pre-war airfields passed through all of these phases, whilst stations opened later in the war should have seen only one. Furthermore, the level and character of defence works seldom correlated with the airfield's status or function. Exceptions are the fighter stations in the summer of 1940 (whose over-defence in relation to others prompted Taylor's enquiry), aircraft storage units from September 1940, and bomber stations in the last two years of the war, where the risk of sabotage was heightened by the station's role in the strategic bomber offensive. What the report makes clear is that most airfield ground defences were erected against invasion, and vulnerability to capture was chiefly a product of site location.
As with earlier projects, the studies now being undertaken will provide the necessary information to guide future management of an increasingly vulnerable, but increasingly valued, part of our heritage. During the year we have attempted to disseminate the results of this survey, and its methodology, to as a wide an audience as possible. Various publications have appeared, notably in Conservation Bulletin and in the journal Antiquity, and the project has been the subject of conference presentations here and abroad. In March we organised a seminar at the Society of Antiquaries which attempted to put this project in its wider context. We have also now distributed the reports from the project's first phase: these have gone to sites and monuments records, the RCHME National Monument Record, as well as some university departments, and selected organisations, institutions, and societies. We hope to disseminate the results of the second phase of the survey within the next two years.