[Graham Boak]

The above figures are for optimum range with the allowance quoted for each Halifax variant - there is no specific statement about reserves for the Stirling. 10% of normal would be a reasonable guide for touchdown at home base - 225gals for the Stirling. I doubt that they have any combat allowance.

Combat radius can generally be taken as being one third of the optimum range, which allows for routing, combat, and perhaps any additional diversion. I know of no source which quotes allowances for such operational details - the routing would be dependent upon target and known enemy defences deployments, plus whatever routing was desired on the Allied side to clear space for night fighter operations, Allied AA, balloon barrages etc. All these factors would vary throughout the war.

A sensible commander would then allow another factor for not all crews being able to obtain optimum performance from their aircraft, either through lack of skill or worn aircraft - or indeed unexpected headwinds in the mission. The sum of these factors might be so limiting that a high-ranking commander may have to decide whether this or that target was so important that risks should be taken, and the factors reduced.

Perhaps a study of individual raids would give an understanding of the level of such diversions. Compare the actual routes flown with the direct distance.