cover 1917 (20 Apr.) envelope from Nyasaland Field Force at Songea to England, bearing uncancelled "N.F." 1d. (on reverse) and showing "FIELD POST OFFICE/9" c.d.s. partly overstruck by framed "MISSENT" h.s., Sudan "FOUND OPEN/OFFICIALLY SEALED" label at top tied by "SHELLAL-HALFA/T.P.O." c.d.s. (28.8), Halfa d.s. (30.8) and triangular censor cachet in violet; some foxing though a rare and most unusual cover. Photo