What did the British flag look like during the American Revolution?

The modern British flag consists of three crosses, one verticle one representing England, and two diagonal ones (St. Andrew's cross) representing Scotland and (St Patrick's cross) representing Ireland.

Ireland was not incorporated into the United Kingdom until the Act of Union in 1801, so the British flag before that date lacked that cross.

The British flag, correctly called the union flag, but also known as the union jack, consists of the flag of England-a red plus cross on a white background,(the flag of St George) The flag of Ireland-a red multiplication, or saltire cross on a white background,(the flag of St Patrick) The flag of Scotland-a white multiplication cross on a blue background. The flag of of Wales, a red dragon on a green and white background was not incorporated into the design.

When the 3 flags are incorporated, Scotland is overlayed by Ireland which is then overlayed by England this produces the union flag. The jack that is sometimes mentioned is the pole that the flag fly's from - ( the jack-staff) If you look closely at a union flag it is possible to identify the three crosses layed on top of each other.

MoreThe Flag flown by the British in the American Revolution is not the Union Jack it shares many of the same qualities but the Union Jack did not come around until 1801.

The pre 1801 Union flag is shown below on the link and would not have had the red St Patrick's cross included in it at the time. It is only called a Union Jack when flown on a ship but the term has entered popular culture. The red cross of St. George represented both England and Wales which were considered a single State and Kingdom.

MoreI would just add that there were also many types of flags flown. Naval Units would hoist a different flag than land forces and we must not forget regimental flags. It was not uncommon for different regiments (units) to have their own flag in addition to the National flag.