||The late 19th century Mobilisation Centre, Fort Halstead, is a Scheduled Monument, Kent 303. It fulfilled its original role as a Mobilisation Centre, a store for armaments and tools for the supply of the volunteer force in the event of invasion, for around decade. During the First World War it may have been used as a store before being sold to a private owner in 1921. In the late 1930s, the site was reacquired by the government and became the Projectile Development Establishment, a remote location for the development of unrotated projectiles (rockets). An experimental filling shed associated with this work is the earliest surviving building associated with rocketry in England. In 1947, Fort Halstead was identified as the headquarters for the ‘High Explosives Research’ team that was responsible for developing Britain’s first atomic bomb. A number of purpose-built structures and buildings associated with this work survive. Globally, these represent some of earliest structures associated with the development of nuclear weapons. This report does not discuss other aspects of Fort Halstead’s wartime work, nor its later post-war research activities.