'Scorpion' was an Allied unrealised plan for a special forces raid by the 'Z' Special Unit on Japanese warships and merchant ships in the harbour of Rabaul on New Britain in the Bismarck islands group to the north of New Guinea (summer 1943).
The 'Z' Special Unit, usually known as 'Z' Force, was a joint Australian, British and New Zealand commando unit, which carried out 284 covert operations in the South-West Pacific theatre. The most well-known of these are the 'Jaywick' canoe raid on Singapore Harbour, and the subsequent 'Rimau' in which all 23 participants were either killed in action or captured and then executed.
The Inter-Allied Services Department was an Allied military intelligence unit established in March 1942 at the suggestion of the commander of Allied land forces in the South-West Pacific Area, General Sir Thomas Blamey. The IASD was based conceptually on the British Special Operations Executive in London, was later renamed as the Special Operations Australia (SOA) and in 1943 became known as the Services Reconnaissance Department (SRD). Several British SOE officers, who had escaped from Singapore, were the nucleus of the IASD, which was based in Melbourne. In June 1942, an IASD raiding/commando unit was organised as 'Z' Special Unit. Several training schools were established in various locations across Australia, the most notable being Camp Z in Refuge Bay, off Broken Bay to the north of Sydney, Z Experimental Station near Cairns, Queensland, Fraser Commando School on Fraser island, Queensland, and Careening Bay, on Garden island, Western Australia.
As a training exercise, one group paddled canoes between Fraser island and Cairns.
In January 1943, Lieutenant S. Warren Carey, an Australian officer and a 'Z' Special Unit officer based at Z Experimental Station, Cairns, Queensland, at the suggestion of Major Ambrose Trappes-Lomax, 'Z' Special Unit’s commander, approached Blamey with the idea of a raid on the Japanese port at Rabaul by a single submarine carrying a small party of commandos. The commandos were to be dropped 10 miles (16 km) off Rabaul, and then use collapsible canoes to reach the harbour, attach limpet mines to as many ships as possible, and then pull back to Vulcan island, where the party would hide until its members could safely rendezvous with the submarine.
Blamey was sure that all the men involved would be captured and shot, but nonetheless approved the operation and authorised Carey to perform whatever actions he deemed necessary during the planning of this 'Scorpion'. By the end of March 1943 Carey had assembled a team of nine men on the Magnetic island base. Lyon and Mott arranged to have Carey’s unit perform a practice attack on Townsville, which had a busy harbour full of troop transports, merchantmen and naval escort vessels. Here tight security was maintained as a result of the threat of Japanese air and submarine attack.
At midnight on 22 June 1943 the unit left its base on Magnetic island and paddled through the heavily mined mouth of Townsville harbour. Dummy limpet mines were attached to 10 ships, including two destroyers. The men rowed into Ross Creek, hid their canoes and travelled into Townsville to find a place to sleep. At about 10.00 the limpet mines were discovered, and panic ensued. Carey was arrested, and despite producing Blamey’s letter and earnest assurances that the mines were dummies, he was allowed neither to leave nor to supervise the removal of the mines, which the Royal Australian Navy feared were real and might have been detonated accidentally. Mott was then able to arrange for Carey’s release, but only on the condition that he left 'Z' Special Unit.
'Scorpion' was scrapped, but Mott and Lyon had nonetheless learned many valuable lessons from the 'raid'.