'Jack' was dubbed Sir Francis in the desert in front of the British press by King George VI and posthumously appointed Commander of the Legion of Merit by U.S. President Franklin D. Roosevelt.

[11] The Dunning Memorial Cup,[12] given annually to the officer that has done the most to further aviation in connection with the fleet, was awarded Linnell in 1920 "... for flights which led to important developments in artillery and reconnaissance observation.

[7][20] After attending Imperial Defence College from the beginning of 1939 until 25 August, he was attached to HQ RAF Bomber Command as Air Officer in Charge of Administration and Mentioned in Despatches[21] in 1940.

[8][22] He was appointed Controller of Research and Development Ministry of Aircraft Production and an additional Member of the Air Council on 5 June of the same year.

[33] Linnell was posthumously invested as a Commander of the United States Legion of Merit in recognition of his outstanding services in the Mediterranean theatre of operations from 29 February – 29 June 1944.

[38] Early in 1943, tests authorised by Linnell in June 1942 at the instigation of Sir Henry Tizard,[38] indicated that a bouncing bomb was technically feasible.

A meeting between the Air Ministry, RAF Bomber Command and MAP decided to continue development of project Upkeep with a proposal to have a fully trained squadron ready by May.

One week later, at a meeting convened by Linnell, the number of Lancasters ordered had risen to a squadron and Operation Chastise was planned for that spring.