Cover with typed 'J. Vermeulen, Postbox 237, London E.C.1' return address on reverse which was the undercover address for the Dutch Army in London franked with pair 1941 2½d light ultramarine GVI issue (SG 489) tied by unclear cds's obliterated by mute circular cancels in purple (applied to disguise the origination of the communication). Addressed to 'Mevr. C.W. Vermuelen, c/o Reguma A,G. Heerbrugg (Kt. St. Gallen) Switzerland' which was the undercover address for the Dutch Army in Switzerland. Censored in the UK with 'OPENED BY EXAMINER 5078 P.C.90' censor strip at left and also in transit in Germany with Nazi censor strip on reverse. Very scarce.