The Australian quarter-ounce gold piece (abbreviated as 1/4 oz and designated with Au for "gold") is a bullion coin format. Uniquely, in Australia there are two mints authorised to strike legal tender: the Royal Australian Mint (which also makes the country's circulating coinage) and the Perth Mint which only makes collector and bullion coins, as well as other bullion products.
Both mints endeavour to create coins with attractive designs, and to introduce new designs and themes often, in order to raise the numismatic value of the coins over the value of previous metal used.
This gold proof coin commemorates the 80th Anniversary of the Battle of Britain.
The Mint says about it:
This remarkable commemorative honours the courageous British and Allied pilots, including 35 Australians, who flew combat operations in the Battle of Britain during the summer and autumn of 1940.
The Royal Air Force’s pivotal struggle against the unremitting attacks of the German Luftwaffe in 1940 is recorded in the annals of history as the Battle of Britain. Young pilots "scrambled" into the air at a moment’s notice, engaging in deadly dog fights with enemy aircraft during several fateful months. Their resolve came at a heavy price, but in refusing to be beaten, they are credited with inflicting the first major defeat on Germany of World War II. | 
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