The Twenty Committee rejected the proposal as too risky and operationally unclear. But it assigned the idea to Ewen Montagu of Naval Intelligence to develop further.
Montagu was a peacetime barrister and King’s Counsel who had volunteered for naval service at the outbreak of war. He ran NID 17(M), a naval intelligence unit focused on counter-espionage and deception involving double agents. He understood both the analytical and operational dimensions of intelligence work in ways that combined his legal training with his wartime experience.
Over the following weeks and months, Montagu and Cholmondeley worked together to transform the abstract proposal into a specific operational plan. The key steps were: finding a suitable body, constructing a credible identity for it, fabricating documents that would serve the deception purpose, identifying a delivery route and recovery mechanism, and assessing the likelihood that the documents would reach German intelligence.
By February 4, 1943, they had filed a revised and detailed plan. The Chiefs of Staff approved it on April 13, 1943. Churchill gave his approval with a characteristically dry comment. When told the plan, he remarked that the Allies would have to get the body back afterward and give it another swim. This was understood as approval. Confirmation from General Eisenhower, the Supreme Commander in the Mediterranean, arrived on April 17.
The operation, now designated Mincemeat, had a brief window. The North African campaign would end in May. The Sicily invasion was scheduled for early July. The documents needed to reach German intelligence in time to affect German operational planning before the invasion force departed its staging areas.