Undercover addresses were used during WWII to conceal the identity and purpose of an establishment. Bletchley Park, an estate in the town of Bletchley, in Buckinghanshire, was the site of Britain's main code breaking establishments, the Government Code and Cypher School. Bletchley Park was allocated undercover address P.O. Box 111, Bletchley.
The covers shown below were mailed from India to Box 111, Bletchley.
Security handstamp 410, February 14, 1944
2 1/2 as. concession surface letter rate to England
July 4, 1945 to P.O. Box 111
8 as. forces air mail rate
1942 Mail to Bletchley
Not Addressed to Box 111
The cover below mailed from Alexandria, Egypt, October 11, 1942, was addressed to L/Cpl. E Kirkman, "Rhonnda House", Bletchley, and not to Box 111, Bletchley. According to Bletchley Park records, L/Cpl. Kirkman was stationed at Bletchley and worked in Hut 5, Hut 7, Block C, and Hut 16 (Intelligence Centre) (Cover Management Team).
Mailed from H.M. Ship, October 9, 1942 to "Rhonnda House", Bletchley
Egypt Postage Prepaid 6 handstamp (Alexandria), October 11, 1942