United States. (Czechoslovakia). 1940. Registered and Advice of Receipt Air Mail envelope addressed to the Czech Republic bearing United States 'Prexie' SG 827, 50c purple tied by concentric ring cachet with framed 'Registered' and hand-struck 'Clipper Air Mail' (struck twice) with oval 'A.R.' on face in violet with New York/ Reg on reverse 'Ap 18 1940' and German censor label tied by circular censor cachet 'e' applied in Frankfurt.