After commissioning, "Oxley" and "Otway" were temporarily assigned to the Royal Navy's 5th Submarine Flotilla. On 8 February 1928, the two submarines set out for Australia in the longest unescorted voyage undertaken by a British submarine. The submarines were diverted to Malta after cracks were found on "Otway"s engine columns. On arrival in Malta, similar fractures were found in "Oxley"s engine columns, and the two boats were detained while improved columns were fabricated and installed. They resumed their voyage in November, and reached Sydney on 14 February 1929. Because of the deteriorating financial conditions leading into the Great Depression, the two submarines were placed into reserve a year later; "Oxley" was paid off into Reserve on 10 May 1930. "Oxley" underwent diving exercises every second week until 9 April 1931, when the submarine was paid off in full prior to transfer to the RN.