Zululand 1879 6d Officers Letter with Inverted Overprint, Rarity

1879 ZULU WAR: OFFICER'S LETTER endorsed "From Capt Cramer 60th Rifles on Active Service Zululand". Sent at the 6d rate paid with Natal 6d OVERPRINT INVERTED (SG 83b). Addressed to Isle of Wight, England. Durban cds 4 8 1879 and Ryde arrival cds SP 4 on reverse. A rare campaign cover, remarkable franking with the invert. VF, most attractive, an exhibition showpiece.