dropped from an altitude of at up to three times the speed of sound at sea level (approximately 3550 km/h). Nevertheless, the threat of what was then code-named "Big Ben" was great enough that efforts were made to seek countermeasures. The situation was similar to the pre-war concerns about manned bombers and resulted in a similar solution, the formation of the Crossbow Committee, to collect, examine and develop countermeasures. Early on, it was believed that the V-2 employed some form of radio guidance, a belief that persisted in spite of several rockets being examined without discovering anything like a radio receiver. This resulted in efforts to jam this non-existent guidance system as early as September 1944, using both ground and air-based jammers flying over the UK. In October, a group had been sent to jam the missiles during launch. By December it was clear these systems were not having any obvious effect, and jamming efforts ended. Anti-aircraft gun system General Frederick Alfred Pile, commander of Anti-Aircraft Command, studied the problem and proposed that enough anti-aircraft guns were available to produce a barrage of fire in the rocket's path, but only if provided with a reasonable prediction of the trajectory. The first estimates suggested that 320,000 shells would have to be fired for each rocket. About 2% of these were expected to fall back to the ground, almost 90 tons of rounds, which would cause far more damage than the missile. At a 25 August 1944 meeting of the Crossbow Committee, the concept was rejected. Pile continued studying the problem, and returned with a proposal to fire only 150 shells at a single rocket, with those shells using a new fuse that would greatly reduce the number that fell back to Earth unexploded. Some low-level analysis suggested that this would be successful against 1 in 50 rockets, provided that accurate trajectories were forwarded to the gunners in time. Work on this basic concept continued and developed into a plan to deploy a large number of guns in Hyde Park that were provided with pre-configured firing data for grids of the London area. After the trajectory was determined, the guns would aim and fire between 60 and 500 rounds. At a Crossbow meeting on 15 January 1945 Pile's updated plan was presented with some strong advocacy from Roderic Hill and Charles Drummond Ellis. However, the Committee suggested that a test not be