British Blue Ensign

The British Blue Ensign is a flag with a blue field and the Union Jack in the upper corner next to the staff. Historically, different colored ensigns (red, white, or blue) indicated a ship's squadron in the Royal Navy. Since 1864, the white ensign is reserved for the Royal Navy and Royal Yacht Squadron.1

Passenger liners and merchant vessels with a specific percentage of Royal Naval Reserve personnel are entitled to fly the blue ensign. Additionally, some British government-owned vessels use it. The Colonial Naval Defence Act of 1865 allowed colonies to "deface" the Blue Ensign with a badge, which often became their de facto national flag before independence. For example, South Australia's Blue Ensign features a magpie, while The Gambia's includes an elephant and palm tree. The Union Jack is incorporated into the canton of the Blue Ensign.1234