WINCHESTER, PORCHESTER CASTLE & PRISON SHIP "GUILDFORD" - VERY RARE 7 YEARS WAR COVERS TO PRISONERS IN P.O.W. CAMP; Fine 9/11 Jan. or 6 Mar. 1759 ELs from London charged "3[d]" with very fine "11/IA" or "6/MR" Bishop Marks on flaps; 19 Jan. 1762 EL from La Rochelle charged "10[d]" (incoming rate ex France) and then "In [all] 1N1" (plus 3d inland ex london) with a mainly fine "MR/1" Foreign Branch Bishop Mark on the flap; and 4 Apr. 1763 EL from London charged "3[d]" with a partly fine "5/AP" Bishop Mark on the flap; and other similar examples dated 1797-1806 to/from prisoners in Porchester Castle or Portsmouth, inc. letters possibly smuggled. Rare early ingoing mail to British POW Camps. All clearly never delivered and thought to have remained in the Paris P.O.'s Secret Office ("Cabinet Noir"). (9 covers) Cross Reference: FRANCE, FRENCH POST OFFICES ABROAD, MILITARY - P.O.W. MAIL, YORKSHIRE (Image)