10/31/2010. Remarks by Johan Visschedijk: "From 1945, when the fully modified Mk.IV made its first appearance, the Firefly assumed notably different external characteristics. The wings were clipped, which improved the rate of roll but detracted rather from the appearance, and the beard radiator disappeared, to be replaced by coolant radiators in extensions of the leading edges of the center section.

A four-bladed Rotal airscrew replaced the earlier three-bladed type, and an extension was made to the leading edge of the fin, increasing its area and improving stability. To complete the transformation, two large fairings appeared beneath the wings: the port fairing housed auxiliary fuel formerly carried in the center section and the starboard fairing carried the radar scanner previously mounted below the center section.

These changes came about as a result of installing the two-speed two-stage supercharged 2,250 hp Rolls-Royce Griffon 74 twelve-cylinder liquid-cooled V-engine, which improved the high-altitude performance considerably, raising the maximum speed by as much as 70 mph (113 kmh). The original testing of a two-stage Griffon engine was in a converted Firefly Mk.I, s/n Z1855, which was re-designated Firefly Mk.III, fitted with a Griffon 61 series engine. This experimental prototype was flown in 1943: it retained similar cowling arrangements to that of the earlier Griffon, resulting in a somewhat bulky nose, which produced unsatisfactory flight characteristics, and the type was abandoned.

In its original form, as flown in 1944, the first prototype Firefly Mk.IV,a converted Mk.I with s/n Z2118, retained the elliptical wing and the original tail assembly. In 1945 it was modified to full Mk.IV standard, and three more conversions were made from the Mk.I airframes (s/n MB649, Z1835 and PP482) for trial installations and further test flying before genuine Mk.IV production began. The prototypes had the 2,330 hp Griffon 72 engine, which was replaced by the Griffon 74 in production aircraft.

The first production Firefly F.R.Mk.IV (s/n TW687) flew on May 25, 1945, and a total of 160 was built (including a small number of N.F.Mk.IV night-fighters), 120 of which went to the FAA of the RN and 40 to the MLD.

Some 43 production aircraft were converted on the line from Mk.I airframes. The last Firefly Mk.IV (s/n VH144) was delivered from the Fairey factory on February 9, 1948. Retrospectively, a number of Firefly Mk.IVs were converted for target-towing duties, being fitted with an M.L. Type G winch under the center section and designated T.T.Mk.IV.

The forty F.R.Mk.IVs (c/n F.8227 to F.8266) for the MLD were delivered between April 18 and October 3, 1947, and initially serialed K-31 to K-70, the 'K' prefix in the serials had been replaced by the number '16' by the time the photo was taken. The aircraft were operated by Squadrons 2 and 4 from the Dutch carrier Hr.Ms. 'Karel Doorman' and British carriers, including the HMS 'Theseus'. Later the aircraft were operated from the Netherlands Antilles and the Netherlands East Indies. The last MLD Firefly was scrapped on December 15, 1961."

A personal note by Jaap de Moor: "At age eleven, 1952,my father, a mechanic, took me to Dutch NAS Valkenburg, I still remember that day vividly. I spent a whole three hours in a Firefly cockpit, dreaming on...., might as well have been in the same 16-47! Now, 16.000 flying hours later, that particular day has always stayed with me as kind of important."