The Union Flag also known as the Union Jack is pictured flying from the Jackstaff onboard a Royal Navy warship.
When the first flag representing Britain was introduced on the proclamation of King James I in 1606, it became known simply as "the British flag" or "the flag of Britain". The royal proclamation gave no distinctive name to the new flag. The word "jack" was in use before 1600 to describe the maritime bow flag.
By 1627 a small Union Jack was commonly flown in this position. One
theory goes that for some years it would have been called just
"the Jack", or "Jack flag", or "the King's
Jack", but by 1674, while formally referred to as "His
Majesty's Jack", it was commonly called the Union Jack, and this
was officially acknowledged.Photographer: LA(Phot) Simmo Simpson
Image 45153521.jpg from www.defenceimages.mod.uk