From 1955 to 1966, Caerwent produced the "Gosling" solid rocket booster for the Seaslug missile. This work began in wartime buildings, the horizontal presses in Press Houses 3 and a longer press in 1, and with other work in a disused blending house and the Tetryl Acetone Recovery building. From 1957 dedicated buildings, J1...J6, were constructed on the eastern side of the site for the production of guided weapons propellants. Buildings J7...J9 at the northern edge of the site formed a static testing site, where these motors could be test-fired. J7 was an environmental conditioning building where charges could be heated to 70 °C or cooled to -40 °C before testing. These buildings were of typical flat-roofed red brick construction, shielded by large earth traverses. Testing work was also carried out here on the "Magpie", "Redtop" and "Sealyham" rocket motors.