Canadian Contingent 1900 OHMS Letter with Contingent Oval

CANADIAN CONTINGENT: 1900 Blue OHMS small format envelope franked GB 1d lilac (APO cds SP 5) to Sherbrooke, Quebec with a fine strike of the CANADIAN CONTINGENT SEP 10 1900 oval in violet. Arrival cds OC 13. Cover with some soiling, otherwise fine, scarce.