Chapter 4 starts with the Mediterranean receiving a new level of recognition in British strategic priority during the August–December 1941 period, becoming the primary effort. Moreover, the anti-shipping campaign was promoted to a prime position in operational priority for the Navy and Air Force, with a corresponding dedication of forces to the task. Coupled with this was an increase in the pace of learning and the refinement of tactical procedures. This led to greatly increased levels of sinkings over August–December, which coincided with a new major British offensive in North Africa: Operation ‘Crusader’. These sinkings successfully denied Axis forces in Cyrenaica the necessary fuel and ammunition to either launch their own planned offensive or to resist the British advance, including the loss of 92 per cent of the fuel shipped in November. Furthermore, the increased levels of attrition meant that sinkings were now greatly outstripping the Axis replenishment capability through new construction or other means. This was the first clear example of the dual effect of the anti-shipping campaign: one operational affecting the war on land in North Africa, and one attritional, undermining the Axis ability to conduct any form of warfare in the Mediterranean. It caused serious concern among the Axis commands, leading to the adoption of new countermeasures, which were to have a major impact in the following year.