[1] In May 1951, faced with reports on the increasingly potential capability of, and thus the threat posed by, the growing Soviet strategic bomber fleet and that nation's newly developed atomic weapons, the British Air Ministry proceeded to draft an Operational Requirement, OR 301, which sought a rocket-powered interceptor that could attain an altitude of 60,000 ft (18,300 m) in just 2 minutes 30 seconds.

Many of the performance requirement laid out by OR 301 was due to the anticipation of rapid increases in performance by the opposing Soviet aircraft; by the early 1960s, it was suspected that these bombers might well be capable of supersonic speeds of up to Mach 2 with a potential operational altitude as high as 80,000 ft.[2] Avro's design team promptly set about designing an suitable interceptor that conformed with the specification's requirements, which would result in the Avro 720 proposal.

[3] Conceptually, the envisioned aircraft was to be operated in a similar fashion to that of the German Me 163, it would use its rocket engine to climb rapidly to meet and engage its target prior to gliding back to earth in a fuel-exhausted state before landing upon a retractable skid arrangement.

[7] The changes contained within the defined specification mainly revolved around armament changes, such as the adoption of the Blue Jay (as it was codenamed at the time) infrared-guided air-to-air missile under development, which replaced the originally-envisaged retractable battery of 2-inch rockets.

[12] However, neither development programmes had managed to secure the backing of the Royal Air Force (RAF), which had been showing signs of hesitancy and had apparent intentions to wait until after both aircraft flight evaluations had been conducted before the service would expressly make any determination on its preference.

[13] From September 1953 onwards, both the Avro 720 and the SR.53 projects were subject to increasing levels of scrutiny amid an overall requirement within the Ministry to implement cuts in order to reduce costs.

Reportedly, official concerns regarding the practicality of using liquid oxygen, which boils at -183 °C (90 K) and is a fire hazard, within an operational environment had heavily contributed to the Screamer's cancellation.

According to aviation author Barry Jones, photographs of the structural airframe, with the port wing fitted and the serial number XD696 painted on, have sometimes been mistakenly claimed to have been of the first prototype.

The Avro 720's main power-plant was an 8,000 lbf (36 kN) Armstrong Siddeley Screamer rocket engine, using liquid oxygen as oxidant and kerosene fuel.