Hopefully we all recognize this as the flag of the UK, and it was on this date in 1606, that royal decree was made for this Union Jack flag to be the official flag of Great Britain. While the term "Union Jack" was not a part of this, it is what we now call this flag. It took the Cross of St. George and superimposed it over the Irish Cross of St. Andrew. This was just called the British flag or the Flag of Britain. It wasn't until around 1674 that the term "Union Jack" came about.