Air Mail cover 1919 (13 March) R.A.F. Experimental Flight Baghdad - Cairo, unfranked envelope bearing a good strike of the framed "POSTAL SERVICE M.E.F./AERIAL MAIL.BAGHDAD - CAIRO/BY 31ST. WING R.A.F. MESOPOTAMIA" h.s. in red, slightly overstruck by "F.P.O.55" c.d.s. in black. Rare. Photo