During the lead-up to D-Day—June 6, 1944—the Allied nations undertook an elaborate deception strategy designed to mislead the Germans about the real date and location of the Normandy invasion. The overall plan was called Operation Bodyguard; one of its more bizarre elements—the creation of a decoy army, complete with inflatable tanks and fake artillery—had the code name Operation Fortitude.
Why Fortitude? As Ben Macintyre writes in Double Cross: The True Story of the D-Day Spies, his 2012 history of the plan:
The choice of code name for this particular operation—the crux of Bodyguard—was much debated. [British Prime Minister Winston] Churchill had given instructions that no code name should be selected that might seem flippant in retrospect or give a hint of the individual or action involved. But he also disliked code names that meant nothing at all, which is why the original choice, “Mespot,” was rejected. Also vetoed were “Bulldog,” “Swordhilt,” “Axehead,” “Tempest,” and, obscurely, “Lignite.” Finally, a name was selected that seemed to evoke the resolution required to pull it off: Operation Fortitude.
It wasn’t only the operations that were deliberately named. The code names of the double agents who worked for MI5, the British intelligence agency, were also chosen with care and a hefty dash of dry humor. Dusko Popov, for example, a risk-loving Serbian playboy, was dubbed “Agent Tricycle.”
This may have been, in part, a reference to Popov’s insatiable appetites and his reputed but probably apocryphal taste for three-in-a-bed sex. It also recognized that the Tricycle network now consisted of one big wheel—Popov—supported by two smaller ones, Agents Balloon and Gelatine.
The Americans took a different approach to code names. When Popov came to Washington in 1941 on an assignment from MI5, FBI Director J. Edgar Hoover, who regarded foreign spies as “just another species of criminal,” was not amused. “The FBI did not go in for jocular code names,” Macintyre tells us. “Popov was ‘Confidential Informant ND 63,’ an austere title that aptly reflects the bureau’s chilly attitude.”