Believed to have been introduced in the reign of Queen Elizabeth I, the sub-division of the English battle fleet into three distinct squadrons lasted throughout the age of sail and was only finally discontinued in 1864. The earliest surviving instructions laying down the wearing of coloured flags to denote the three squadrons date from 1617 and under these, the admiral's squadron flew a red ensign, the vice-admirals's a white, and the rear-admiral's a blue. As fleets grew in size and the squadrons became correspondingly larger, it gradually became impossible for the commanding admiral to control the movements of an entire fleet. Thus, command of each constituent part devolved upon the admirals of the squadrons which were ranked in order of red, white and blue. Likewise, admirals took their rank according to the colour of thir squadron and promotion was granted using the same progression of colours.