China India New South Wales 1901 cover to Annandale with India 1a 'C.E.F.' opt tied by 'FIELD P.O. No.1' Bridge-type CDS Boxer Rebellion

1901 cover to Annandale with India 1a 'C.E.F.' opt tied by 'FIELD P.O. No.1' Bridge-type CDS , reverse with 'BASE OFFICE/B' Hong Kong, Sydney and Annandale backstamps. There is no endorsement to indicate whether this cover is from the N.S.W. Contingent to the Boxer Rebellion, or from some other writer. The N.S.W. Contingent left China in March 1901. A rate incoming cover from this conflict, few years at top caused by opening, otherwise fine