Blue Ensign

Blue Ensign
Use	State ensign
Proportion	1:2
Adopted	1620 (as the flag of the Blue Squadron; 9 July 1864 (as used by vessels authorised by warrant);
Design	A blue field with the Union occupying one quarter of the field and placed in the canton.

The Blue Ensign is a British ensign that may be used on vessels by certain authorised yacht clubs, Royal Research Ships and British merchant vessels whose master holds a commission in the Royal Naval Reserve or has otherwise been issued a warrant. Defaced versions with a badge or other emblem are also more broadly; in the United Kingdom by authorised government or private bodies; and internationally by nations or organisations previously a part of the British Empire.

The evolution of the Blue Ensign followed that of the Union Jack. The ensign originated in the 17th century with the St George's Cross (the Flag of England) in the canton, and with a blue field.

The Acts of Union 1707 united England (which included present day Wales) with Scotland in the Kingdom of Great Britain, thus producing a new Blue Ensign with the new Union Flag, containing a saltire, in the canton. With the Act of Union 1800, Ireland became a part of the new United Kingdom of Great Britain and Ireland, and St Patrick's Cross was incorporated into the Union Flag and, accordingly, into the cantons of all British ensigns from 1 January 1801.

The modern Blue Ensign of the United Kingdom
The British Blue Ensign (1707–1801)
English Blue Ensign as it appeared in the seventeenth century