The "Highball" device was intended to bounce across the sea until it hit an enemy ship, sank and exploded.

The Mosquito selected for the conversion work to carry "Highball" was the Mk.IV series II: the work entailed removing the bomb bay doors and equipping the aircraft with specialised carriers enabling them to carry two "Highballs", each weighing 1,280 lb (580 kg), in tandem.

For this role 25 Mosquito B.Mk.IVs were further modified: The squadron's primary target was designated as the Kriegsmarine Surface Fleet, primarily the battleship Tirpitz, so the squadron remained training in Scotland and waiting for the Surface Fleet to sortie into the North Sea until July 1944, when this threat had lessened.

In August 1944, the squadron deployed to RAF Beccles in Suffolk, and in September changed aircraft again to Mosquito Mk.XVIs.

[1] In order to keep up aircrew proficiency and safeguard the modified Mosquitos, 12 disassembled FB Mk VIs were also sent, arriving in Sydney in February 1945.

Training began at Narromine that month A detachment was sent to British Pacific Fleet base at Manus Island in March, but the squadron was unable to go into action against Japanese shipping, mostly because there was no target left in the area anymore.

[2] Due to political-strategic infighting between the British Pacific Fleet and the U.S. military, the unit was never in action, and was disbanded (officially) at RAAF Station Narromine on 14 July 1945.