Union (National) Flag of Great Britain
The Union Flag is the national flag of Great Britain. It is more properly called the ‘Great Union’, established by royal proclamation of April 12, 1606. It was formed by a combination of the crosses of St. George and St. Andrew; at the union with Ireland in 1801, the cross of St. Patrick was added. It is essentially the military flag of England. It is flown as the war jack on the jackstaff of English warships.
John H. Finley ed. Nelson's Perpetual Loose-Leaf Encyclopaedia (vol. 5) (New York, NY: Thomas Nelson and Sons, 1917)