The St George’s Cross defaced with the arms of Dunkirk flown from the jack staff is the warranted house flag of the Association of Dunkirk Little Ships. It is known as the Dunkirk jack. The flag is flown only by civilian vessels that took part in the Dunkirk rescue operation.
The operation is the evacuation of Dunkirk during WWII.
My dad served in WWII in an American Army Service Battery. I do not think he saw Dunkirk, but he did mention possibly the worst part of the whole thing was being at sea surrounded by only water and boats.
An upcoming film, Dunkirk, explores this bit of history partly from the point of view of one of the small civilian craft that helped evacuate the Allied forces, as well as from air and land viewpoints.
apparently it was also a film in 1958 and a British docudrama in 2004.
Dunkirk is scheduled to be released on 21 July 2017 in IMAX. The film is a co-production between the Netherlands, the United Kingdom, France, and the United States
Twelve boats used during production had once taken part in the actual Dunkirk evacuation