On one operation during World War 1 Australia lost half of it's submarine fleet. While that sounds worse than it actually was, it's true. The HMAS AE-1 was one of the only two submarines Australia had at the beginning of World War 1. Both the AE-1 and her sister AE-2 were British E-Class submarines built at Vickers and sent to the Royal Australian Navy in 1914.

Both boats were under repair when the war started and were completed rapidly. The first mission for the AE-1 was to escort a convoy to Port Moresby which was completed successfully. The next assignment was to patrol the waters between Rabaul and Cape Gazelle. Sometime after departing Rabaul on Sept. 14, 1914 the AE-1 sank for unknown reasons. To this day the loss of the AE-1 and her 35 crew is a mystery. The boat has never been found although several searches have been made. The AE-1 was the first allied submarine lost in World War 1. Her sister AE-2 was lost April 30, 1915 after being attacked by a torpedo boat the captain and crew scuttled her. In this case the entire crew was saved and were interned in Turkey where four died in captivity.

A British E Class submarine, same type as AE-1.