Posted to M Special Unit of the Services Reconnaissance Department, Siffleet was on a mission in Papua New Guinea when he and two Ambonese companions were captured by partisan tribesmen and handed over to the Japanese.

A photograph of Siffleet's impending execution became an enduring image of the war, and his identity was often confused with that of other servicemen who suffered a similar fate, in particular Flight Lieutenant Bill Newton.

[1][3] Allotted to a signals company based at Ingleburn, New South Wales, he was reported absent without leave on two occasions; he was by this time engaged to Clarice Lane.

of the A.I.F., young and competent",[5] Siffleet joined a party led by Sergeant Thijs Staverman of the Royal Netherlands Navy, which included two Ambonese privates, H. Pattiwal and M. Reharing.

Siffleet signalled Fryer to warn him of the hostile natives and of Japanese patrols, indicating that he was preparing to burn his party's codes and bury its radio.

They were ambushed by a hundred native villagers near Aitape and, after a brief melée during which Siffleet shot and wounded one of their attackers, the group was captured and handed over to the Japanese.

[10] The photo was published in Australian newspapers and in Life magazine but was thought to depict Flight Lieutenant Bill Newton, who had been captured in Salamaua, Papua New Guinea, and beheaded on 29 March 1943.