The Ruck machine gun post or Ruck pillbox is a type of hardened field fortification built in Britain during the invasion crisis of 1940–1941. It was designed by James Ruck and was made from prefabricated concrete sections and paving slabs, sandbags and rammed earth. The Ruck machine gun post was relatively widely used in Lincolnshire and along the east coast of England, but is now extremely rare with just a handful of extant examples. Today, just five Ruck machine gun post sites are recorded in the Defence of Britain database.