The only known copy of this datestamp being used. Referenced by Kenny and Crabb (History of the British Army Postal Service) with the note not seen. Not recorded by Edward Proud in his similar publication. 

Plain cover to London (opened three sides) cancelled with the single ring FIELD POST OFFICE 51 datestamp 10 MY 18 - allocated to 51 Brigade 17 Division in security exchange phase 4. I would assume used by the Division as a spare or counter datestamp. 

Unit censor (T6) No 4734

Condition as shown; Opened three sides

ID: GB WW1 40435