The story of the Vulcan began with a post war specification, which called for an aircraft to carry a 'special bomb' (nuclear weapon), of large linear dimensions, weighing 10,000 lb (4,536 kg) to a target 1,725 miles (2,780 km) miles away at a cruising speed of 576 mph (927 km/h), at heights of up to 50,000 ft (15,240 m). Still air range was to be 3,858 miles (6,209 km), and gross weight was not to exceed 100,000 lb (45,360 kg). This final requirement focused the design team's attention on ways of reducing weight, which eventually led to the delta wing design, which was tested using the Avro Type 707.