The Experimental Filling Shed (Building F11) at Fort Halstead was built in 1938 and is the earliest surviving purpose-designed building associated with rocketry research and development which was established at Fort Halstead (Monument HOB UID 407330) in 1937 to accommodate the Projectile Development Establishment. The location provided a remote and contained site for rocket development building on earlier work by the Ballistics Branch based at the Royal Arsenal in Woolwich. From the late 1930s the site expanded with a number of buildings constructed inside and outside the fort. Building F11 was designed in February 1938 and erected in the same year, and is probably the earliest surviving building in the new research establishment. It was designed to allow the filling of cordite rocket motors. It is a two-storey concrete-framed building encased in brick and L-shaped on plan, with a sloping concrete framed roof. Its principal elevation faces east which has an external metal stair leading to a first floor covered walkway. Internally the southern half of the building is occupied by brick-built vertical filling bays to accommodate rocket casing for the assembly of a 9 foot rocket.The Experimental Filling Shed at Fort Halstead is a grade II listed building. For the designation record of this site please see the National Heritage List for England.