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