The Blue Ensign is a flag, one of several British ensigns, used by certain organisations or territories associated with the United Kingdom. It is used either plain, or defaced with a badge or other emblem.
The evolution of the Blue Ensign followed that of the Union Flag. The ensign originated in the 1600s with the St. George's cross (see Flag of England) in the canton, and with a blue field background (top right).
The Act of Union 1707 united Scotland, England and Wales in the Kingdom of Great Britain and produced a new blue ensign which placed the Union Flag in the canton. With the Act of Union 1800, Ireland joined the United Kingdom and the St Patrick's Cross was added to the Union Flag of the United Kingdom and, accordingly, to the cantons of the British ensigns from 1 January 1801.
Prior to the reorganisation of the Royal Navy in 1864, the plain blue ensign had been the ensign of one of three squadrons of the Royal Navy, the "Blue Squadron." This changed in 1864, when an order in council provided that the Red Ensign was allocated to merchantmen, the Blue Ensign was to be the flag of ships in public service or commanded by an officer in the Royal Naval Reserve, and the White Ensign was allocated to the Navy.
Thus, after 1864, the plain blue ensign is permitted to be worn, instead of the Red Ensign, by two categories of civilian vessel:
* British merchant vessels whose officers and crew include a certain number of retired Royal Navy personnel or Royal Navy reservists, or are commanded by an officer of the Royal Naval Reserve in possession of a Government warrant. The number and rank of such crew members required has varied over the years, as have the additional conditions required, since the system was first introduced in 1864.
* Yachts belonging to members of certain long-established British yacht clubs, for example the Royal Northern & Clyde Yacht Club. Permission for yachts to wear the blue ensign (and other special yachting ensigns) was suspended during both World War 1 and World War 2.