The critical Allied defeats of 1940 had left the British geographically isolated and confined to a traditional strategy of naval blockade and peripheral ground campaigns, such as that developing in North Africa, designed to wear down a Continental enemy. By 1941, the aircraft involved in the 1940 purchase programme and the consequent ‘3,000 per month’ plans behind Lend-Lease had been clearly directed towards relieving British aircraft production from this peripheral commitment. Yet that commitment was becoming increasingly marginal to British plans for the future. The strategic bombing offensive waged against Germany now became central to British strategy, and obtaining the heavy bombers necessary for expanding this campaign became a new focus of Anglo-American aircraft supply diplomacy after 1940.

Intensifying the strategic bombing campaign required the dedication of enormous production resources. In the first place, wastage, or the loss of aircraft on operations, was substantial. As an example, between July and November 1941, Bomber Command lost 526 aircraft on operations – the equivalent of its entire frontline strength. The most efficient policy to secure the quantity of replacement aircraft needed was to expand further the production of existing types. But this conflicted with the RAF's desire to improve aircraft quality, most notably by the introduction of heavy bombers to replace the medium bombers in service in 1940.