Air Fronts: Theaters of Operation - ETO -  AP 156: Battle of Britain - 3. Aircraft

THE BATTLE OF BRITAIN. Air Ministry Pamphlet 156; Issued by the Department of the Air Member for Training, August 1943

MACHINERY OF OPERATION

III. Aircraft *

British Fighters

The performance of our single-seater fighters varied with the type of propeller fitted and the boost pressure used. Three types of propeller were fitted both to the Hurricane and Spitfire - (i) two-blade wooden fixed pitch, (ii) variable pitch propellers which could be operated by the pilot either to coarse or to fine pitch, (iii) constant speed propellers, i.e. which could be set to rotate at a constant speed by the pilot depending on the power it was desired to obtain from the engine. The change to the constant speed propeller made little, if any, difference to the maximum level speed of the aircraft, but it did considerably shorten the take-off run, increase the rate of climb and the ceiling and make the aircraft more manoeuvrable at heights.

The engine in both the Hurricane and Spitfire was the Merlin III. It normally operated at a boost pressure of + 61 lbs., but an override control was fitted which allowed the pilot to obtain 12 lbs. boost for emergencies. Above 15,000 feet the full emergency boost pressure of 12 lbs. could not be obtained, and the maximum boost obtained at 18,000 feet was 61 lbs. The increase in boost from 61 lbs. to 12 lbs. gave a considerable increase in speed at low altitudes. The following table shows the effect of boost on speed when flying level: -

Both the Hurricane and the Spitfire could stand a tremendous amount of punishment and still remain under control and capable of bringing their pilots back, while the Merlin engine was extremely reliable. And it is interesting to remember that the Luftwaffe was fought almost entirely on this Merlin engine.

Armament. Both aircraft were fitted with 8 Browning .303 machine guns mounted in the wings clear of the propeller, 4 on each side. Those in the Hurricane were spaced at smaller intervals than those in the Spitfire. The 20 mm. gun did not come into use during the Battle of Britain.

Armour. By the start of the Battle of Britain all our single-seater fighters, with very few exceptions, were fitted with bullet-proof windscreens. By July practically all Hurricanes and most Spitfires had front armour; this filled up the unprotected space between the bottom of the bullet-proof windscreen and the top of the engine. Most of the aircraft had rear armour by the middle of July, but some were still being fitted with it during August.

Self-sealing Tanks. The Hurricane had one gravity tank in the fuselage, and one main tank in each wing. None of these were self-sealing before the Battle of Britain started; the wing tanks were dealt with early, being covered with a self-sealing fabric known as Linatex; the fuselage tank was left uncovered at first, since it was thought that it would be protected by the front armour, but as the result of experience it was also produced with the self-sealing cover. The change of tank was carried out on squadron aircraft after about the middle of September. The Spitfire carried its fuel in two intercommunicating tanks in the fuselage just in front of the pilot; neither of these were self-sealing to start with. During the battle self-sealing lower tanks were produced covered with Linatex, but self-sealing could not be applied to the upper tanks owing to lack of clearance. The lower tanks were replaced in squadrons as fast as their other work allowed, and before the end of September new and repaired Spitfires were being received with self-sealing on the lower tank.

There was only one squadron of Defiants in the Battle of Britain. This was a single-engine two-seater aircraft, the gunner being seated behind in a power-operated turret carrying 4 Browning machine guns. It had some striking successes before the Battle of Britain, but proved to be unsuccessful against fighters and was relegated to night work or to the attack of unescorted bombers.

The Blenheim was a twin-engine multi-seater and was unsuitable for daytime combat with fighters owing to its low speed and lack of manoeuvrability and for these reasons it was employed on night duties. There was also one squadron of Gladiators still in use and located in the West. This aircraft was very manoeuvrable and had done good work in Norway against bombers, but it was too slow to compete with the Messerschmitts.

Radio-Telephony

Only a small proportion of the fighters in the Battle of Britain were equipped with Very High Frequency (V.H.F.); most of the R/T was carried on with ordinary High Frequency (H.F.). The fact that under these circumstances good R/T communication with aircraft was maintained speaks highly for the R.A.F. signals staff on stations. Changing over to V.H.F. was carried on during the battle. This was not an easy task, since it is impossible for a leader to control his squadron by R/T if some of the aircraft have V.H.F. and some H.F., therefore all the aircraft needed to put up a squadron formation had to be changed simultaneously. The fact that some squadrons were fitted with H.F. and some with V.H.F. introduced complications, since communication between an aircraft fitted with the one and a ground station fitted with the other was not practicable.

German Aircraft

The Me.109, a single-engine single-seater, was originally fitted with 4 rifle calibre machine guns, 2 firing through the propeller, and one in each wing clear of it. In the spring of 1940, Me.109 appeared with two 20 mm. cannon in place of the wing machine guns, and it is probable that during the Battle of Britain about half were of the 4 machine-gun type and half of the cannon version.

By July the Me.109 was being fitted with an armoured bulkhead just behind the petrol tank, i.e. about 5 feet behind the pilot. Further protection was given to the pilot by two other plates, one just behind his neck and head, the other curving over the back of his head. The latter interfered with the pilot's view, and in consequence was often removed. It will be noted that the armour only gave protection from astern. The tanks were not self-sealing.

Me.110. This had two 20 mm. cannon and four rifle calibre machine guns all fixed and firing forward. The only rear defence was one machine gun in a somewhat primitive mounting in the rear upper position. Early in the Battle of Britain the Me.110 was fitted with armour to protect the pilot against fire from the front, during the autumn of 1940 an attempt was made to protect the aircraft against attacks from astern by mounting an armour plate behind the gunner, and a bullet-proof windscreen was also supplied for the pilot. The petrol tanks of the Me.110 were self-sealing.

The He.113 had a better performance than the Me.109, but it is doubtful if it was ever used in the Battle of Britain except for high altitude reconnaissance. Quite a small number had been built up to the end of October 1940, and it seems probable that the Germans used it largely for propaganda purposes since it was frequently written up in the German-inspired neutral Press.

The armament of the German bombers was poor. They had no power-operated turrets till late in 1941: at the beginning of the war they had only three machine guns, but by the autumn of 1940 the number had been increased to six or even more. The additional machine guns were fitted in makeshift swivel mountings firing to the side and below; the He.111, for instance, had a total of seven machine guns, two in the nose, one in the rear upper and two in the rear lower position, and two mounted laterally firing through side windows. Their armour was gradually increased during the Battle of Britain so as to provide protection for all the crew, and the weight of armour carried was about 500 lbs. by the end of 1940. The petrol tanks were self-sealing from the start of the war. The majority of the He.111 and Ju.88 aircraft destroyed were brought down by hits in the engine. Further details of German aircraft are given in Appendix A.

Comparison of the Opposing Aircraft

The two great advantages that the Hurricanes and Spitfires possessed over the different types of Messerschmitt were first their superior manoeuvrability, especially when they were fitted with the constant-speed propeller, and secondly the fact that they carried 8 machine guns. This armament was, of course, much superior to the 4 machine guns that the Me.109 originally possessed, and proved, during the battle, to be superior to the combination of 2 machine guns and 2 cannons.

In making a comparison of performance it must be remembered that the Me.109 was modified and given more powerful engines during the battle, and that towards its end both the Me.109 and Me.110 were being fitted with engines having an improved supercharger. This gave greatly increased power, and consequently better performance, at heights of 18,000 feet and over. Different types doubtless appeared over this country simultaneously.

Although the newer type of Hurricane and Spitfire was being issued to squadrons before the end of October, 1940, the comparison below is drawn only with the Hurricane I and Spitfire I. It is assumed that 12 lb. boost was used for speed and 6 1/4 lb. boost for climb.

Relative Performance

Hurricane against Me.109

Speed and climb about the same as the original Me.109, but inferior to the later versions, especially in speed.

Hurricane against Me.110

Speed slightly lower and climb slightly superior up to 18,000 feet. When the Me.110 had engines with the improved supercharger it was superior at heights over 18,000 feet, in climb as well as in speed, and this was more marked the greater the height.

Spitfire against Me.109

Speed definitely and climb slightly superior to the original 109, and equal to that of the later versions up to 20,000 feet, above which the Me.109 had the better climb.

Spitfire against Me.110

Much superior in speed and climb up to 20,000 feet, but when the Me.110 had engines with the improved super-charger its speed and climb over 20,000 feet was superior to that of the Spitfire, and again the superiority was more marked the greater the height.

Normally the Hurricane was used below 18,000 feet and the Spitfire above that height; in consequence the Hurricanes generally encountered the enemy bombers, whereas the Spitfires generally met the enemy fighters.

The Me.110 was considered by pilots to be easier to deal with than the Me.109.

The Hurricane I was faster and had a better climb than any of the German bombers. It was generally agreed that the eight machine guns constituted the best armament for the attack of enemy bombers until such time as a large amount of armour was fitted to the latter.

The relative value of speed, climb, good view, armour and armament in fighter aircraft is a subject for constant argument, but weight of fire in a given time is always an important factor, and was especially so in the Battle of Britain. It was not only that the period of time during which a pilot could keep his sights on an enemy fighter was very short, but that if a pilot having got into a good position astern of an opponent continued to remain there for more than 2 or 3 seconds, he would almost certainly be himself attacked from astern by another enemy fighter.

Many factors, such as location and tactical employment, influenced the work of the different types of fighter aircraft and should be taken into account in making a comparison of their success. But it may be of interest to record that the total number of enemy aircraft brought down by the single-seater fighters was in the proportion of three by Hurricanes to two by Spitfires. The average proportion of each type serviceable each morning was approximately 63 per cent. Hurricanes and 37 per cent. Spitfires,

In proportion therefore to the numbers available, Spitfires brought down about 6 per cent. more than the Hurricanes.

The Constant Speed Propeller

Fitting the constant speed propeller to Spitfires and Hurricanes undoubtedly contributed to the result of the Battle of Britain, and also affords a good example of the wholehearted co-operation on the part of the aircraft industry.

The conversion did not entail making new propellers but only fitting new parts in the propeller hub. The work was carried out by the well-known firm of de Havilland. The first proposal for this was telephoned to the firm on Sunday, 9 June. The first parts were ready in four days, and the actual conversion was effected at a fighter airfield during the same night as the Germans were rejoicing over their entry into Paris. The test flight showed the advantage, especially in climb and ceiling, that was given by the constant speed propeller. On 22 June, work in quantity commenced, de Havillands taking on the manufacture of all the conversion parts required, although normally some of these would have been supplied by other manufacturers. The work was done without any contract, and as late as March 1943 the firm was still being called upon to produce evidence that certain aircraft had in fact been converted. The firm promised to manufacture and deliver 20 sets daily starting on 24 June, and this promise was kept. Conversion was carried out at fighter airfields without interfering with the operations. The method was as follows: de Havilland would send one of their engineers to each airfield with the conversion sets, the first conversion was done by the firm's man, the second by an R.A.F. crew with his help, and the third by the R.A.F. under his supervision, after which the R.A.F. carried on on their own. The first aircraft to be ready was tested by a de Havilland test pilot, who also explained the working of the constant speed propeller to the fighter pilots. By the beginning of August, just before the heavy German attacks began, all the Spitfires had been converted and the Hurricanes were finished by 16 August.

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* For reasons of space reference to the aircraft of Bomber and Coastal Command is omitted.