Interesting section from 'Destiny in the Desert' by Jonathan Dimbleby.
It was at this moment that, serendipitously, the code-breakers at Bletchley Park discovered that Fellers’s coded messages from Cairo had been decrypted by Axis intelligence. It is impossible to establish the precise impact of this embarrassing discovery on the outcome of the Anglo-American talks – which had already been substantially recast by the fall of Tobruk – but, according to the American historian C. J. Jenner, who has sifted the available evidence, ‘Whitehall handled Washington’s disgrace, which was decisive in appalling loss of British blood and treasure, with adroit magnanimity.’ From Jenner’s account it appears that Churchill cleverly turned America’s mortification to British advantage. Instead of reproaching Roosevelt for the Fellers debacle, he allowed the disgrace merely to hang in the air as he strove to secure the President’s endorsement of his own strategic priorities.
Whether or not remorse for the role that Fellers had inadvertently played in the loss of Tobruk did in fact play a significant part in American calculations, Churchill came away from Washington with every reason to be satisfied with what had been achieved. Sledgehammer had been postponed at least until 1943, Gymnast was still in the frame for 1942, and the Eighth Army was about to be massively reinforced with 300 of the latest and best tanks in the world. He could congratulate himself that, while Roosevelt saw very nearly eye to eye with him over future strategy in the region, the President’s advisors, some of them seething at the way in which – as they saw it – ‘Our Boy’ had been manipulated by Churchill – had clearly been worsted. Paradoxically, so far from the humiliation at Tobruk weakening Churchill’s hand, it had evidently had the opposite effect.