Thomas Welsby Clark was a sailor in the Royal Australian Navy (RAN), whose body was found on a life raft in the Indian Ocean, near Christmas Island, on 6 February 1942.

Clark was formally identified by DNA analysis in 2021, and the RAN publicly released his identity on 19 November 2021, the 80th anniversary of the battle.

[4] Christmas Island's assistant harbour master, Captain E. Craig, stated that "the Carley float was typical of those in service with the RN and RAN".

[7] In 2019 it was incorrectly reported by news media that Norman Douglas Foster was most likely to be the Sydney crew member in question.

[8] Foster, who was 28 years old at the time of Sydney's sinking, was an Engine Room Artificer, 4th Class (a rank equivalent to Petty Officer).

[9] During the late afternoon of 6 February 1942, 79 days after Sydney sank, lookouts on Christmas Island spotted an object out at sea.

[10] Initially thought to be a Japanese submarine, closer inspection from a pilot boat found it was a Carley float with a dead person inside.

[10] With the island at risk of invasion, the deceased was quickly examined by the harbour master, the medical officer and the man in charge of the radio station.

[12][13] An inquest was not convened until mid-February and had not concluded when evacuation began on 17 February in anticipation of Japanese forces occupying the island on 23 March.

[14] A preliminary examination in 1942 by the island's medical officer, Dr J. Scott Clark, found that the deceased was a tall young adult male caucasoid.

[15] The remains were partly decomposed, the eyes, nose and all of the flesh from the right arm were missing and believed to have been consumed by fish or birds.

[16] According to the Harbour Master, Captain J. R. Smith, the body was clothed in a blue boilersuit which had been bleached white by exposure, with four plain press studs from neck to waist.

For many years, other authors, such as historian Barbara Winter (1984) and independent researcher Wes Olson (2000), disputed the official view put forward by the RAN.

[25] Following an autopsy and sampling from the body for identification, the remains of the still unknown sailor were reburied in the Commonwealth War Graves section in the Geraldton Cemetery in Western Australia with full military honours on 19 November 2008.

Bone isotope analysis showed that he had lived in eastern Australia, probably New South Wales or Queensland, before enlistment and may have grown up on the coast.

[25] As squatting was unusual at the time in urban western communities, it was speculated that the man had spent significant time in a rural area of Australia, amongst members of an ethnic group in which squatting was more common than sitting (such as people from Asia or Eastern Europe), and/or involved in a sporting or similar activity that required the ankles to be flexed towards the back of the thighs for prolonged periods.

[31] Analysis of the partial genetic profile recovered suggested that the man had red hair, blue eyes and pale skin, and was likely of Irish or Scottish descent.

This relatively rare haplogroup has most often been found in people with matrilineal ancestors from various parts of Europe, the Caucasus or Middle East.

[6] Tests on the remains of the boilersuit showed that the fabric had never been dyed, was probably white and the press studs were of a type manufactured by Carr Australia Pty Ltd in the 1930s and 1940s.

While veterans did not recall being issued with them or seeing them worn, photographs of RAN personnel from the period show some of them wearing white canvas shoes.

[32] In August 2019, it was reported by media outlets including Channel 7 News and The West Australian, that the Sydney crew member most likely to have been buried on Christmas Island was Norman Douglas Foster.

[9] Foster's service record describes him as 5 ft 83⁄4 in (174 cm) tall, with auburn hair, blue eyes and a fair complexion.