QEII   Mixed usage (graphite/non-graphite) used outside of (Southampton) experimental area. Postage = 6d (per oz) plus 1/- registry fee. Postage consists of 1st Graphites Edward/Crown SG565 (S54) 2½d Type II Carmine-red x 6 (2 Pairs + 2 singles), Plus 1 x SG544b (S53) Edward Crown 2½d Type I (located second in from right, bottom row),  Plus 1 x SG540 (S2) Edward Crown ½d Orange-red On Registered Mobile PO No 3  Cover Derby. Cancelled with single ring "Mobile Post Office No 3" 26th March 1958. Posted to Swarthmore PA  USA. Back has Swarthmore Pennsylvania  receiving stamp dated 10th April 1958.  Wmk orientation has not been ascertained so assumed upright for ref purposes. Note: scans form part of the description.  (Our Ref: 2317)