Churchill was a solid strategist, at least on a macro level. Also, fortunately for England, he tended to avoid involving himself on tactical decisions (Gallipoli was instructive in this, no doubt).
Churchill's single greatest contribution to Britain's success was to help manipulate/team up with FDR to bring the USA in on Britain's side. Months before Pearl Harbor, the USN was already coordinating and to some extent fighting the Battle of the Atlantic with the UK. With US resources available, it became almost impossible for Britain to lose. Hiter's decision to declare war on the USA after Pearl Harbor made it that much easier -- but Churchill had already worked that field and was bringing in the harvest.
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