This led to Air Ministry specification E.3/45. The winning design, the Canberra, also dispensed with defensive armaments, producing a design with the speed and altitude that allowed it to fly past most defences. The design's large wings gave it the lift needed to operate at very high altitudes, placing it above the range where even jet powered fighters were able to intercept it. The Canberra could simply fly over its enemy with relative impunity, a quality that made it naturally suited to aerial reconnaissance missions. The design was so successful that it was licensed for production in the United States, one of very few such cases. The Martin RB-57D and F American-built reconnaissance subtypes further extended the wings up to a 37.5 span, compared to the much more modest British PR.9 Canberra having just a 20.2 meter wingspan.