The Dunkirk Jack is the House Flag of the Association of Dunkirk Little Ships, under permission of the Admiralty, the College of Heralds and the City of Dunkirk.  The jack consists of the Cross of St. George (the flag of Admiralty) defaced with the Arms of Dunkirk. This jack can be worn by Member Ships at any time when the owner is aboard.  Member Ships are limited to civilian vessels that took part in the Dunkirk rescue operation between 27 May and 4 June 1940.
Two public domain sources were used to create this file: https://en.wikipedia.org/wiki/File:Flag_of_England.svg and https://en.wikipedia.org/wiki/File:Blason_ville_fr_Dunkerque_(Nord).svg
David B. Gleason