The anniversary of the proclamation of the Statute of Westminster is celebrated every year on December 11th. Where facilities permit, federal buildings, airports, military bases and other federal institutions within Canada shall display the Royal Union flag, commonly known as "Union Jack," together with the national flag, From sunrise to sunset, to highlight this day. "Facilities" means the existence of at least two masts. The flag of Canada always takes precedence and should never be replaced by the Union Jack. If there is only one mast, no special arrangements are made to have a second mast installed to deploy Union Jack on this special day.
The 1931 Statute of Westminster (an act of the British Parliament) affirmed Canadian autonomy and recognized the almost complete independence of the dominions which in fact existed in principle since the First World War and the resulting Treaty of Versailles. In addition to being a truly significant milestone in our evolution as an independent nation, the Statute of Westminster of 1931 can be seen from various angles as the foundation or charter of the present Commonwealth.