The flag of Ireland is a tricolour of green, white and orange. The flag originates with the Young Ireland movement of the mid-19th century but was not popularised until its use during the Easter Rising of 1916. The colours represent the Gaelic tradition (green) and the followers of William of Orange in Ireland (orange), with white representing the aspiration for peace between them. It was adopted as the flag of the Irish Free State in 1922 and continues to be used as the sole flag and ensign of the state. A naval jack, a green flag with a yellow harp, is set out in Defence Forces Regulations and flown from the bows of warships in addition to the national flag in limited circumstances (e.g. when a ship is not underway). It is based on the unofficial green ensign of Ireland used in the 18th and 19th centuries and the traditional green flag of Ireland dating from the 16th century.