The Tett turret is a type of hardened field fortification built in Britain during the invasion crisis of 1940–1941. It was a small circular pillbox named after its inventor H.L. Tett and manufactured as a private commercial venture by Burbridge Builders Ltd of Surrey. It comprised a revolving concrete turret mounted on a ball race that allowed it to be turned easily. The turret was set above a pit; in early designs, the pit was formed by a standard section of concrete pipe in diameter.