On 14 November 1939, the liner was requisitioned by the RAN for use as an armed merchant cruiser (AMC).
The AMC conversion consisted of the addition of seven 6-inch main guns, two 3-inch anti-aircraft guns, and equipment to operate a Supermarine Walrus amphibious aircraft.
Manoora was commissioned into the RAN on 12 December 1939, although the conversion was not completed until 5 February 1940.
She was assigned the pennant number F48.

Initially, the ship was used to patrol Australian waters, but during March 1940, she was redeployed to the China Station to operate with the Malaya Force.
During the ship's return to Australia in early April, Manoora intercepted four Norwegian merchant vessels and escorted them to Brisbane; Norway having recently fallen to the Germans, and the Allies wanted to ensure as many Norwegian-flagged vessel came under their control as possible.
On 12 June, shortly after Italy became involved in the war, Manoora intercepted the Italian passenger vessel Romolo, which was scuttled off the Solomon Islands.
The AMC then provided assistance to United States cargo ship Admiral Wiley, which had run aground at Kitava.

Between the end of 1940 and September 1941, Manoora's operated around the north and east coasts of Australia, around New Guinea and New Britain, and to the Solomons, Nauru, and Ocean Island.
In December, the AMC transported Admiral Sir Guy Royle to Singapore, then transited to the Bay of Bengal for escort duties.
On 1 March 1942, the ship left Colombo for Australia, with a convoy of troopships returning from the Middle East.
On 14 November 1939, the liner was requisitioned by the RAN for use as an armed merchant cruiser (AMC). The AMC conversion consisted of the addition of seven 6-inch main guns, two 3-inch anti-aircraft guns, and equipment to operate a Supermarine Walrus amphibious aircraft. Manoora was commissioned into the RAN on 12 December 1939, although the conversion was not completed until 5 February 1940. She was assigned the pennant number F48.
Initially, the ship was used to patrol Australian waters, but during March 1940, she was redeployed to the China Station to operate with the Malaya Force. During the ship's return to Australia in early April, Manoora intercepted four Norwegian merchant vessels and escorted them to Brisbane; Norway having recently fallen to the Germans, and the Allies wanted to ensure as many Norwegian-flagged vessel came under their control as possible. On 12 June, shortly after Italy became involved in the war, Manoora intercepted the Italian passenger vessel Romolo, which was scuttled off the Solomon Islands. The AMC then provided assistance to United States cargo ship Admiral Wiley, which had run aground at Kitava.
Between the end of 1940 and September 1941, Manoora's operated around the north and east coasts of Australia, around New Guinea and New Britain, and to the Solomons, Nauru, and Ocean Island. In December, the AMC transported Admiral Sir Guy Royle to Singapore, then transited to the Bay of Bengal for escort duties. On 1 March 1942, the ship left Colombo for Australia, with a convoy of troopships returning from the Middle East.
HMAS Manoora (F48)