The Australian Navy's Appleleaf-class underway-replenishment oiler HMAS Westralia , shown here earlier this year, returned from her last overseas deployment in April 2006 and was decommissioned in September, following the early conversion and delivery of her replacement, HMAS Sirius . One of a class of four merchant tankers, the Sirius was formerly named Delos before being purchased by Australia in 2004 from Tsakos Energy Navigation Ltd., of Athens, Greece, for 50 million U.S. dollars. The contract for the design and modifications necessary to convert her to a naval vessel was also issued in 2004. Between July 2004 and August 2006, the Sirius underwent conversion to become a naval auxiliary. In addition, the fifth Armidale-class patrol craft, HMAS Pirie , was commissioned on 29 July 2006, while the 13th and 14th units of the class, to be named the Gleneg and Marysborough respectively, have been ordered and are expected in service by 2009.