Later recruited to the Special Operations Executive, he worked in Scandinavia - both behind enemy lines in occupied Norway and in neutral Sweden - as a spy and saboteur; after the war, he claimed he had been responsible for the explosion in a German munitions train, though the veracity is suspect at best.
After a harrowing escape, recounted in his wartime memoir Sweet is War, he was put in charge of SOE's activities in Southern Italy, where he participated in the Anzio landings.
In Southern Italy, he took the mimicry further, dressing as a (large) old lady to smuggle a radio transmitter past German lines and coordinate SOE activity in the occupied zone.
[4] After an abortive attempt at a political career with the Conservative Party, Munthe re-directed his work towards maintaining the family homes in England, Sweden and Italy.
He sold his father's remaining properties on Capri (the Villa Materita, inter alia), and bought the Castello di Lunghezza, a 108-room castle outside Rome.