ABSTRACT
The War Potential Letter, twice amended since its fractious inception in 1951, was again amended on 27 July 1961, the Committee emphasising the purpose of the revised restrictions was ‘to safeguard the deterrent and to preserve secrecy on classified weapons and military equipment required for waging limited war.’ 212 Thomson’s letter reiterated that the prohibited list included, until officially announced and only with prior advice ‘from the appropriate Department’, all new weapons and equipment. A tougher prohibition still was placed on details of code name, design, performance and maker, and on rates of output, numbers ordered, trials and stocks of nuclear weapons, guided missiles, aircraft, weapons, vehicles, warships, and electronic equipment. The same restrictions on the publication of aerial photographs without prior consultation were repeated, but now applied only to Defence (including USAF) sites and to factories developing new weapons and equipment, of which the appendices listed 25 industrial airfields and 33 contractor companies. 213
