Blue Steel remained the primary British nuclear deterrent weapon until the Royal Navy started operating Polaris ballistic missiles from Resolution-class submarines.

During the early 1950s, the Soviet PVO-Strany interceptor aircraft and its associated ground controlled interception systems were steadily improving, making the approach to the V bomber's targets more difficult.

One was to fly higher and faster, but the leap in performance needed to overfly the missiles, with altitudes on the order of 70,000 feet (21 km) could not be met until the mid-1960s at the minimum.

Avro, having recently given the go-ahead on the 730, appeared cool on the long-range concept and was primarily interested in a short-range weapon of perhaps 100 miles (160 km) range, which would allow it to avoid the most heavily defended areas.

Handley Page's concept rejected the MoS's shorter range and offered a design of 500 nautical miles (930 km; 580 mi) using ramjet power.

However, the Ministry noted that the inertial navigation system (INS) being developed by Elliott Automation would not be accurate enough to fly this distance and hit its targets within the desired circular error probable (CEP).

[7] Vickers, who had worked on the somewhat similar Blue Boar and Red Rapier projects would seem like the natural choice for the contract, and planned to have their weapon in operation two years earlier than the other teams.

Avro appears to have been selected due to a number of RAE personnel having been hired by the company to form their design department, the Weapons Research Division, including the Chief Engineer, R.H. Fransis.

To achieve the desired 1 MT yield, the implosion had to be extremely symmetrical, and this required a 72-point explosive system that led to the weapon being 45 inches (1,100 mm) in diameter and massing an estimated 4,500 pounds (2,000 kg).

It was the large size of the warhead, and the resulting 48 inches (1,200 mm) diameter fuselage needed to carry it, that led Avro to the use of a rocket motor when most standoff weapons to that point were jet or ramjet powered.

In Stage 1, the 13,000 pounds (5,900 kg) weapon would be powered by a two-chamber rocket engine that would provide the required 100 nautical miles (190 km; 120 mi) range at speeds up to Mach 2.5.

The 16,000 pounds (7,300 kg) Stage 2 would use an improved engine and more fuel to provide range up to 240 nautical miles (440 km; 280 mi) at speeds up to Mach 4.5.

Stage 3 would weigh in at 25,000 pounds (11,000 kg) and include both disposible boosters and a drop-off fuel tank with range up to 450 nautical miles (830 km; 520 mi).

The wings and canards became deltas and the experience of the Bristol 188 gave Avro confidence in construction of rounded surfaces using stainless steel and the design became much more aerodynamic with a boat tail and ogive nose.

[9] The project was delayed by the need to develop the required stainless steel fabrication techniques; this would have been gained in building the Avro 730 but that had been cancelled by then.

The UK sought to acquire the much longer-ranged United States AGM-48 Skybolt air-launched ballistic missile and was greatly frustrated when that weapon was cancelled in late 1962.

The Royal Air Force estimated in 1963 that half the missiles would fail to fire and would have to be dropped over their targets, contradicting their purpose of serving as standoff weapons.

A stop-gap weapon (WE.177B) was quickly produced to extend the life of the V-bomber force in the strategic role until the Polaris missile was deployed.