From Edward Marsh, ed., Ambrosia and Small Beer: The Record of a Correspondence Between Edward Marsh and Christopher Hassall (London: Longmans, 1964)—
A soldier up for medical exam proved to have been wearing a truss for the past six years, and was classified as P.E. or Permanently Exempt. On his way out he gave this news to his pal, who immediately asked for the loan of the truss, which was granted. The examiner asked how long he had been wearing it, and he said "Six years," whereupon he was classified as M.E. "What's that?" he asked. "Middle East." "How can I go to the Middle East when I've been wearing a truss for six years?" "If you can wear a truss for six years upsidedown, you can jolly well ride a camel for six months."