Formation No. 618 Squadron was first formed at
RAF Skitten on 1 April 1943, as part of
No. 18 Group of
Coastal Command, from crews of
No. 105 Squadron RAF and
No. 139 Squadron RAF. The unit was initially equipped with
Beaufighter Mk.II fighter-bombers, but quickly changed to converted
Mosquito Mk.IVs.
The Highball The "Highball" device was intended to bounce across the sea until it hit an enemy ship, sank and exploded. Unlike the cylindrical
Upkeep weapon used by
No. 617 Squadron RAF in
Operation Chastise, the "Highball" was more spherical. 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. The bombs were designed to skip across water and to provide weapon stability and accuracy. Before release they were spun backwards at 700 to 900 rpm by a
ram air turbine mounted in the bomb bay's midsection, fed by an extendable air scoop. The bombs were to be dropped from a maximum altitude of 60 ft (20 m) at a speed of 360 mph (600 km/h). In the event, through lack of weapons, training and aircraft, No. 618 Squadron was kept frustratingly inactive and never attacked the
Tirpitz. Instead, the unit was selected for carrier-borne operations in the Pacific. For this role 25 Mosquito B.Mk.IVs were further modified: • Each aircraft was equipped with Merlin 25s, adapted to provide peak power at low altitudes, driving four-bladed
Rotol propellers: these propellers had narrower blades than the standard three-bladed units, meaning that the engines would rev up faster and respond quicker to throttle movement, factors vital in the limited length of carrier takeoffs. • Longer intakes under the engine cowlings were fitted with tropical filters. • The undercarriage legs were made of heavier-gauge metals and the wheels were fitted with the twin brake units of FB Mk VIs. • The rear fuselages were structurally modified with a special internal
longeron and reinforced bulkheads designed to take the additional loads imposed by carrier landings: an additional bulkhead (No. 5a) was fitted. • Externally a "V-frame" arrestor hook was fitted. The "snap gear" which released the hook was operated by a
Bowden cable from a lever mounted on the cockpit port side. • An access hatch was moved from the starboard rear fuselage to underneath, and an extra longitudinal stiffening strake, identical to that already fitted to the starboard side of production Mosquitos, was fitted to the port fuselage. • The tailwheel fork pivots incorporated end plates to avoid being caught in the arrestor cables. • Armoured windscreens were fitted, along with hydraulic wipers. • Three PR.Mk.XVIs, which were to be used for reconnaissance duties were also fitted with the four-bladed propellers and fuselage modifications for carrier operations.
UK squadron movements 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. As a matter of fact, the German Surface Fleet never emerged from its bases in
Norway. In the meantime, the squadron had moved to
RAF Wick and re-equipped with Mosquito Mk.VIs and No. 618 Squadron did not have had the opportunity to use the "Highball" weapon. In August 1944, the squadron deployed to
RAF Beccles in
Suffolk, and in September changed aircraft again to Mosquito Mk.XVIs. The squadron deployed to
RAF Benson in September, transitioning to Mosquito Mk.XVIIIs in October.
Australian deployment In December 1944, No. 618 Squadron was deployed to Australia for carrier-borne operations, as Japanese targets for the "Highball" weapon were still available there. These Mosquitos were transported to Australia on board the carriers and , arriving on 23 December 1944, subsequently sent to the de Havilland Australia's
Mascot,
Fishermans Bend aircraft factory for reassembly. 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. 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. The converted Mosquitos were stripped of all military equipment and sold off. The sole surviving No. 618 Squadron Mosquito, an FB. Mk.VI
HR621, is currently undergoing restoration at the
Camden Museum of Aviation. ==Aircraft operated==