HISTORY

flying Gloster Gauntlet biplanes.

The re-equipment commenced on August 11th, the last, sixteenth Spitfire

was delivered to the squadron as late as November 16th, 1938. In October the re-equipment started at No. 66 Squadron also based at Duxford

and close to the end of the year the first two Spitfires were received by

No. 41 Squadron at Catterick airfield. Till the end of 1939 the deliveries

reached 49 Spitfires Mk.I. Due to the deterioration of the international situation, on September 1st the Air Ministry increased the orders of Spitfires

by 200 aircraft. Further contracts for 200 and 450 airframes respectively

followed on April 20th and August 9th, 1939 and as early as on April

12th, 1939 the Air Ministry signed the contract with Morris Motors Ltd.

for 1000 license-built Spitfires Mk.II constructed in the new factory in Castle Bromwich. In the spring and summer 1939 the production was finally

gaining the necessary pace. On September 3rd, 1939, day the Great

Britain entered the War, 11 Fighter Command squadrons were equipped

with Spitfires. Absolutely crucial for the successful deployment of the new

fighters in the upcoming war was continuous elimination of the technical

faults and their restriction on the already delivered and factory-fresh

Spitfires. First production Spitfires were powered by twelve cylinders Rolls

Royce Merlin II engine with 768 kW (1060 hp) single stage single speed

compressor. It was driving the two blade wooden Weybridge propeller.

Starting with 78th production airframe (K9961 manufactured on May

8th, 1939) Spitfires Mk.I were equipped with three blade two speed

metal De Havilland Type 5/20 propeller which was also installed on the

aircraft originally furnished wit two blade propeller. Starting with the

airframe serialed K9980 (May 16th, 1939) the production Spitfires Mk.I

were powered by a new, more reliable Merlin III engines of the same

output, cooled by water-glycol mixture (70:30). Merlin II and Merlin III

engines‘ standard fuel was 87 grade aviation gas DTD 230. Significant

Spitfires Mk.II from Castle Bromwich as well as Hurricanes Mk.I were given priority in the installation of Rotol propellers. Practically the only unit

fully equipped with Spitfires Mk.I featuring Rotol propellers was No. 54

Squadron operating from Hornchurch during the winter 1939/40. As the

performance of the aircraft furnished with constant speed propellers was

significantly better than that of those featuring two speed propellers, the

solution was found in the conversion of two speed De Havilland propellers

to constant speed ones. Modifications were performed by a team of technicians from De Havilland directly at the units‘ level, conversions took place between June 24th, 1940 and August 16th, 1940 on all Spitfires Mk.I

and Hurricanes Mk.I equipped with two speed propellers De Havilland

5/20. Later, the constant speed De Havilland Type 5/39A propellers

were installed as a standard. During their whole service life Merlin engines suffered from oil leaks, problem which has never been fully resolved.

The carburators were also causing trouble due to the fact that during the

negative G maneuvers, such as sharp transition into the dive flight, they

were failing and briefly interrupting the fuel mixture supply for the engine. Problem was solved relatively later, after the Battle of Britain, having

introduced so-called RAE-restrictor which was in fact a well-known and famous modification of the carburator float invented by Ms.Beatrice Shilling.

Visually important modification was application of the bubble cockpit

canopy. It is said that it was implemented on the production lines in January 1939 but supposedly it appeared on some individual airframes

several months earlier because at least one Spitfire Mk.I belonging to No.

19 Squadron featured this type of canopy already in October 1938.

The problem was very difficult, even impossible, opening of this cockpit

canopy during the flight in the case of the necessity to bale out of the

No 611 Squadron Spitfire Mk.I equipped with armored windshield.

modification of Merlin III allowed the option to burn 100 grade American fuel which, in conjuction with higher manifold pressure, increased the

engine output primarily at the lower flight altitudes. The modification was

continuosly being introduced since the spring 1940 but the capability to

use 100 grade fuel was the standard feature of Merlins XII powering

Spitfires Mk.II, Merlins III were factory-modified for this fuel since September 1940.

damaged aircraft. In order to equalize the cockpit pressure a small hatch

was added to the canopy, a notorious crow bar was added to the cockpit

door and later Martin Baker canopy emergency release system was implemented. Modifications were performed on the front line aircraft only

during Battle of Britain period.The rear mirror mounted on the canopy

windshield was introduced in order to improve the Spitfire‘s rear field of

vision. Initially it was installed at the units‘ level, later as a standard equipment on the production lines and as a retrofit according to the official modification. The gunnery tests shown that the machine guns were freezing

at the higher altitudes. The solution was the installation of the gun heating

by means of the hot air ducted from the larger air cooler located under

the right wing. The modification was incorporated the production lines

starting with 60th manufactured airframe (K9846) in January 1939 and

retrofitted to previously built aircraft. Later, the hot air guns heating was

replaced with an electrical system. During the introduction of Spitfire Mk.I

the armament of eight Browning 7.7 mm machine guns was considered

powerful and respectable but in the course of time, with introduction of

cockpit armor and self-sealing fuel tanks it became insufficient and further

development to increase the Spitfires‘ armament impact was by introducing 20 mm cannons. Spitfire Mk.IB modification was armed with 20 mm

cannons and manufactured in relatively small numbers since the fall 1940.

In October No.19 Squadron received delivery of the first combat ready

Spitfires Mk.IB. Important and welcome modification was introduction of

the incendiary de Wilde ammunition for Browning machine guns.

Merlin III allowed the installation of the constant speed three blade Rotol

RMS.7 propeller (license-built Hamilton Standard Hydromatic) with which

a smaller number of Spitfires built in the end of 1939 was furnished.

Gunsights are directly linked to the armament. First Spitfires were equipped with simple mechanical aiming device, a circular sight in the cockpit

and vertical sight in front of the windshield. This was soon replaced with

No 19 Squadron Spitfires equipped with late type of the Pitot tube, and already by the

hot-air gun heating.

INFO Eduard - August 2020

eduard

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