The Pickett-Hamilton Fort was designed to maximize surprise on attacking German invaders attempting to secure airfields. In four seconds, the fort would rise up out of the ground and level machine guns at paratroopers landing at Bomber Command airfields. The cost of the fort was right - about £240 (£8,729 in 2005 dollars - about $16,195) However, several practical problems prevented the actual use of the fort. No one could resupply the fort during a firefight - they would have to cross an open airfield during a battle. Also the fort could not support the weight of heavy bombers. Finally, many were positioned in such a way that they interfered with the normal flight operations of the airbase in the "up" position. During drills, when they were occupied for the first time in a while, wastewater from rains and condensation would accumulate, making the use of these forts very annoying for their two to four crewmembers. Before the war was even over Bomber Command stopped using these forts. Over 375 were installed before they quit.