Editing Blue Steel (missile) (section)

===Avro's concept===
At the time, [[nuclear weapon]] design was still in its early stages, and the intended weapon for the missile was a [[boosted fission]] weapon known as "Green Bamboo". 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 {{convert|45|inches}} in diameter and massing an estimated {{convert|4,500|lbs}}. This weapon was secret and only the diameter and mass were revealed to prospective entrants. It was the large size of the warhead, and the resulting {{convert|48|inch}} 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. Avro simply could not find a place to put an air intake on the missile which did not result it in being too large in some other dimension, typically length. The engine, the [[Armstrong Siddeley]] [[Armstrong Siddeley Stentor|Stentor Mark 101]], had two chambers, one for cruising at about Mach 1, and a second larger one that was ignited close to the target to increase speed to Mach 3 for a final dash.

At Mach 3, [[skin friction]] will heat the fuselage to around {{convert|315|to|480|C}}, which is higher than the temperature that will cause [[aluminium]] to become soft. This is the reason that most high-speed aircraft are generally limited to about Mach 2.4 or lower, flying above this speed risks damage to the airframe. Those aircraft that do operate above this speed have to use other materials, and for this role, Avro chose [[stainless steel]]. The difficulties encountered bending sheets of stainless steel led to initial designs for the weapon that were very "linear", with the fuselage made of a single sheet rolled into a cylinder and a second sheet rolled into a cone to form the nose area.

Avro's initial response, in late 1955, outlined a four-stage development effort. In Stage 1, the {{convert|13,000|lb}} weapon would be powered by a two-chamber [[rocket engine]] that would provide the required {{convert|100|nmi}} range at speeds up to Mach 2.5. The {{convert|16,000|lb}} Stage 2 would use an improved engine and more fuel to provide range up to {{convert|240|nmi}} at speeds up to Mach 4.5. Stage 3 would weigh in at {{convert|25,000|lb}} and include both disposible boosters and a drop-off fuel tank with range up to {{convert|450|nmi}}. For the future Avro 730, a new delta wing design of 18 to 26,000 lbs would offer range up to {{convert|900|nmi}}.{{sfn|Gibson|Buttler|2007|p=105}}

Considering their submissions, the Ministry responded by ordering Avro to work only on the OR.1137 requirements, and ignore the long-term developments. This produced the first complete design, W.100. They proposed building the missile from AF.520 stainless steel, expecting to learn how to do so using the 730 contract to build testbeds. A series of smaller designs, W.101 through 104, would be made from a variety of materials and used to test the flight dynamics, [[autopilot]] and INS. As part of ongoing industry-wide research, the design underwent several evolutionary changes. The wings and canards became [[delta wing|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.{{sfn|Gibson|Buttler|2007|p=109}}