With the invasion of Belgium and Holland and the dropping of paratroops to secure key targets, the British realized that the RAF airfields needed defenses to protect them against ground troops. The Royal Army didn't like this design, so most were installed at airfields. The turret could fire all sorts of machine guns and anti-tank rifles out of its shuttered front access slot, or open the top port to fire against aircraft. The turret would be set in a brick-lined dugout and could traverse a complete 360 degrees, but it was hard to turn and fire at the same time and track targets. 200 of these turrets were installed around the United Kingdom. After the war most were reclaimed for their metal, so this a rare example.