One prototype, JF321, was fitted and tested with a Rotol six-bladed contra-rotating propeller unit; although this promised to eliminate the characteristic swing on take-off (caused by the propeller slipstream) the propeller unit was prone to failure. The pitch control mechanism controlled the pitch on the front propeller, A similar contra-rotating propeller unit was later used on production Seafire 46 and 47s. When the new fighter entered service with 610 Squadron in December 1943 it was a leap forward in the evolution of the Spitfire. Jeffrey Quill flew the first production aircraft, RB140 in October 1943: The Mk XIV could climb to in just over five minutes and its top speed, which was achieved at , was . In operational service many pilots initially found that the new fighter could be difficult to handle, particularly if they were used to earlier Spitfire marks. Don Healy of 17 Squadron, based at Madura recalled that the Mk XIV was; ...a hairy beast to fly and took some getting used to. I personally preferred the old Mk Vs from a flying standpoint ... Even with full aileron, elevator and rudder, this brute of a fighter took off slightly sideways. In spite of the difficulties pilots appreciated the performance increases. Wing Commander Peter Brothers, O/C Culmhead Wing in 1944–1945 and a Battle of Britain veteran; It was truly an impressive machine, being able to climb almost vertically – it gave many Luftwaffe pilots the shock of their lives when, having thought they had bounced you from a superior height, they were astonished to find the Mk XIV climbing up to tackle them head-on, throttle wide open! F Mk XIVs had a total of 109.5 gal of fuel consisting of 84 gal in two main tanks and a 12.5 imp gal fuel tank in each leading edge wing tank; other 30, 45, 50 or 90 gal drop tanks could be carried. The fighter's maximum range was just a little over on internal fuel, since the new Griffon engine consumed much more fuel per hour than the original Merlin engine of earlier variants. By late 1944, Spitfire XIVs were fitted with an extra 33 gal in a rear fuselage fuel tank, extending the fighter's range to about on internal fuel and a 90 gal drop tank. Mk XIVs with "tear-drop" canopies had 64 gal. As a result, F and FR Mk XIVes had a range that was