In response, Aldermaston developed a new warhead called Red Beard that was half the size of Blue Danube and weighed one-fifth as much, mainly through innovation in the pit design, principally the use of an "air lens". Instead of the core being immediately inside the tamper, there was an air gap between them, with the core suspended on thin wires. This allowed the tamper to gain more momentum before striking the core. The concept had been developed by the Manhattan Project in 1945 and 1946, and permitted a reduction in both the size of the core and the amount of explosives required to compress it.