The Australian half ounce silver piece (abbreviated as 1/2 oz and designated with Ag for "silver") is a bullion and commemorative 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 coin marks the 30th anniversary of the Sister City relationship between Houston and Perth. In 1984, the cities of Houston, Texas in the United States and Perth, Western Australia in Australia joined together in an official partnership as Sister Cities.
The historical foundation for this partnership went much further back than 1984 however. During the Battle of Sunda Strait in World War II, the USS Houston and HMAS Perth formed a joint American-Australian task force that attacked a superior Japanese naval force in hopes of delaying Japanese movements toward Australia. Both ships were sunk that day, but succeeded in stalling the Japanese Navy long enough for the American and Australian navies to regroup and halt the Japanese advance entirely. | 
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