The first Blenheim Mk I prototype, K7033, flew on 25 June 1936 from Filton. On 10 March 1937, the first aircraft began arriving at 114 Squadron, followed by 30 Squadron in Iraq on 13 January 1938, and India the following spring. Bristol released a description of their new aircraft:
[A] high speed day bombing landplane. The crew of three consist of the pilot, housed in the front fuselage, a bomb aimer/navigator whose station is alongside the pilot on the starboard side, and the wireless operator/gunner, in the rear fuselage. A bomb cell under the centre plane which forms an integral part of the fuselage, provides means for the carrying of various bombloads… The bomb fuses are set and released by electrically operated gear. A Vickers gun, operated by the pilot, is mounted in the port outer wing and has a Lewis gun… in the rear fuselage turret.
The bomb release system was very simple: the w eight of the falling bombs pushed the bomb bay doors open, and the doors then snapped shut by elastic cabling, which did have an effect on accuracy, but no more so than the Heinkel He 111, whose bombs were dropped tail first.
Defences on the bomber were not extensive, with the forward firing gun being operated by a button mounted in the pilot’s control column but this was nothing more than a strafing tool or to scare off enemy aircraft. The Blenheim’s main firepower was the more vulnerable machine gun, mounted in a turret on the upper fuselage. Bristol claimed that the turret had been specially designed for the aircraft and fitted with a retractable hood:
It is circular structure with the necessary mechanism to train the gun over a wide field of fire, centralising near the stern. The turret has a bypass valve by a spring clip lever on the main control handle in addition to its control valves. This returns the pressure oil to the supply when the operator releases the handle, so that the turret operates automatically if the gunner is disabled.
The weapon mounted in the turret was the Vickers ‘K’ gas-operated machine gun, which was a development of the Vickers Berthier used by the Indian Army. The Vickers ‘K’ had a fire rate of between 950–1,200 rounds a minute and was faster than the German MG 34, which was being fitted to the Luftwaffe’s bombers. More importantly, it was more reliable than the Brownings, but had problems with space due to the ammunition pan getting in the way of aircraft structures.
As demand for the aircraft grew, Bristol subcontracted the design out to Avro and Rootes Securities in England, and the design was also picked up by foreign markets in Finland and Yugoslavia, who were given licence to build their own; these exports were sold to Turkey, Greece, and Romania. By the commencement of hostilities, some 1,351 Mk I Blenheims had been produced in Britain alone before the Mk I was discontinued in favour of the Mk IV.
There were a few design faults with the Mk I that needed ironing out, with the first being a small range, as well as cramped cockpit conditions. In the Mk I, the control yoke obscured the view of the pilot’s controls, and the engine instruments obscured the pilot’s views on landing and take-off. To make matters even worse, the propeller controls were actually behind the pilot and were operated by the pilot on feel alone. This was hardly an efficient way to fly a combat aircraft, and so Bristol began looking at the evolution of its airframe. After abandoning the Mk II, they test-flew a Mk III model with an elongated cockpit, allowing the bomb aimer much more space and better visibility for the pilot. Fuel tank space was increased; the Vickers ‘K’ replaced with two Brownings to give the gunner greater firepower; and the new Mercury XV engines, which generated 920 hp were added, creating a top speed of 266 mph at 12,000 feet. So rushed was the order for aircraft, due to the rising political tensions with Germany, that the first Mk IVs to be built were equipped with Mercury Mk VIII engines, as the newer engines had not been delivered. The first Mk IVs began arriving in early 1939, by which point it was known that the top speed of Germany’s and Britain’s fighter aircraft far exceeded the top speed of the Blenheim, but nothing else was available. The top speed was fast enough for it to be able to defend itself especially if flying in formation.
July 1934 saw the issuing of Specification B.3/34 for a heavy land-based night bomber and transport aircraft to replace the Handley Page Heyford biplane, which could carry a 2,500-lb bombload up to 920 miles at 142 mph, and the Fairey Hendon, who could carry 1,660 lb a maximum 1,360 miles at 152 mph. After complaints from the various aircraft factories, the design teams’ requirement for ‘transport’ was dropped and the aircraft was given over to be solely a bomber. The chief designer of Armstrong Whitworth, John Lloyd, created the A.W. 38, which was a development of an earlier, rejected, design: the A.W. 23 bomber/transport. The A.W. 23 first flew on 4 June 1935 and was a low wing monoplane with a ‘portly’ frame and a fabric-covered tubular steel frame powered by two 840 hp Tiger VIIIs, with the novelty retractable landing gear defended by two nose and tail Lewis guns. It ultimately lost to the Bristol Bombay as a troop transport, but the prototype was later used as a testbed for inflight refuelling before its destruction during the Battle of Britain in an air raid.
The new aircraft, dubbed ‘Whitley’ after the main Armstrong Whitworth factory, was built around the Armstrong Siddeley Tiger IX radial engines, which generated 795 hp with the innovative de Havilland three-bladed two-position variable pitch propellers. However, this new feature caused a certain amount of design problems. in that Lloyd was not familiar with flaps on wing design, and so at first did not put the new propellers in, but, under pressure, altered the wing angle to an 8.5-degree angle of incidence to maintain a good performance at take-off and landing. Flaps were later introduced, but the wings were left as they were, giving the aircraft its familiar nose-down profile at cruising level, but also causing a fair amount of drag. The aircraft’s designers were also not concerned with any aesthetic niceties and sleek aerodynamic lines, giving the Whitley what has been referred to by some pilots as an ‘ugliness’ that causes unnecessary drag, and an almost ‘ponderous, graceless form’
The Whitley was the first aircraft in the RAF’s growing arsenal to use a semi-monocoque fuselage with the loads supported by the external skin of the aircraft, with a light, basic airframe inside the fuselage, rather than a hefty airframe covered with a linen skin which affected performance. Armstrong Whitworth also tried to ease construction methods by using a slab-sided structure rather than a tubular fuselage, and it was this airframe that was considered able to withstand quite a bit of damage and still be airworthy, something that aircrews would come to rely on over Germany at night.
By June 1935, the RAF were getting concerned about their ageing bomber fleet and wanted to update them quickly due to fears of Ernst Heinkel’s He 70 being a good candidate for bomber conversion and the formidable He 111’s first test flight on 24 February 1935. A contract for eighty aircraft was issued, with half being Mk Is and half Mk IIs. Construction began at various Coventry sites, including the former Ordinance works and Whitley Abbey, before final assembly at Baginton aerodrome.
It was not until 17 March 1936 that the first prototype, the Tiger-IX-powered K4586, flew from Baginton, with A. C. Campbell Orde in the cockpit. The second prototype (K4587) was equipped with the supercharged Tiger XIs. The first production run of thirty-four Whitley Mk Is were delivered to 10 Squadron, armed with Vickers machine guns mounted in the nose and tail turrets and a bombload of 3,365 lb.
With the production of specification B.21/35 underway, modifications of the airframe were made. This created the Mk II, which was powered by two 920 hp Tiger VIIIs, and then, under specification 20/36 issued on 4 August 1936, the Mk III saw further evolution, with the Vickers guns being replaced with a Nash-and-Thompson-powered turret fitted with belt-fed Browning 303s. There was also a retractable ventral turret with a pair of Brownings but this was found to cause a lot of drag and was heavy, with crews often finding them difficult to pull back into the aircraft when at height in the cold. The Mk IV saw the replacement of the Tiger engines with the Rolls Royce Merlin IV with an increased horsepower of 1,030, a top speed of 245 mph, and an altitude of 16,250 feet. The Merlin X was also put into the Mk IVa, increasing the horsepower to 1,145. The Mk IV’s tail armament increased to four Brownings in a Nash and Thompson turret, with revisions to the nose shape (to incorporate a better bomb aimer position) giving the Whitley a pointed chin and an increase of fuel load and range. The variant that Bomber Command took to war was the MK V, fitted with the Merlin X and which had a lengthened fuselage (by 1 foot and 3 inches), allowing the rear gunners a greater field of fire while the tail fins were reduced in size and the twin rudders area was increased to improve handling. The Whitley was considered obsolete by the time war commenced but it was more than adequate as a night bomber, as it was not envisioned to face enemy fighters, and the rugged reliable design was considered more than capable of delivering a bombload to German industry from the invulnerable night sky while the Wellingtons and Hampdens delivered by day.
The RAF specification P. 27/32 was issued in 1934, looking for a light bomber to replace the aged Hawker Harts, Furies, and Hinds. The specification outlined the need for a two-seater aircraft that could carry a 1,000-lb bombload a distance of 1,000 miles at 200 mph. Fairey, Armstrong Whitworth, and Hawker all put forward designs.
The Armstrong Whitworth A.W.29 was a mid-wing cantilever monoplane constructed with a forward fuselage of welded tubular steel and a monocoqued light alloy rear. It was powered by the radial Armstrong Siddeley Tiger VIII engine, which generated 870 hp and had a top speed of 225 mph or a cruising speed of 208 mph. The crew of two sat separated, with the pilot along the wing’s leading edge, while the observer gunner was aft of the spar in an enclosed manually operated turret with a Lewis gun. The pilot had control of another Vickers gun in the wing as well as the 1,000-lb bombload. It was not a very attractive aircraft in comparison to the Fairey submission, which had been designed by the Belgian Marcel Lobelle.
The Battle was a modern sleek design, with more emphasis on the lines and elegance than for crew comfort. One navigator would later lament that there was very little room in the rear cockpit, and that the gunner was pretty much sat right on top of you. There was also a fuel tank right beside you, which caused more than a little concern.4 The first prototype’s gunner position was also poorly designed, and the glazing meant the gunner would suffer from a lot of down draught—the pilot’s cockpit was more roomy and comfortable, but it had a tendency to overheat.
The Battle was the first aircraft to be fitted with the new Rolls-Royce Merlin engine, the same engine that would equip Hurricanes, Spitfires, and Lancasters. The Mk I sported 1,050 hp and was tapered into the fuselage, which gave the Battle a top speed of 257 mph, and a cruising speed of 210 mph.
The fuselage was the first Fairey aircraft to have a stressed metal skin over the gently tapering oval sections and all metal wings. The armament was similar to the Armstrong Whitworth craft and consisted of a solitary Browning machine gun mounted in the starboard wing and fired by the pilot, and a gas-operated Vickers ‘K’ in a Fairey high-speed mounting in the rear of the cockpit. This position was exceptionally exposed and, with modern fighters like the Hawker Hurricane Mk I sporting eight Browning 0.303s rather than the two Vickers 0.303s on the Bristol Bulldogs it was replacing, the Battle’s defence was already looking flimsy in 1937. By 1940, the Fairey Battle had to be sidelined, as fighter design and armament had rapidly evolved, leaving the Battle’s solitary Vickers to grow even more important. The Messerschmitt Bf 109E variants not only sported machine guns but also a MG FF cannon, while the heavier Bf 110 carried four nose-mounted machine guns and two MG FF cannon.
Hawker’s Henley design was a combination of a light bomber and dive bomber, using a lot of the Hurricane’s design as a basis as they already had a basic, versatile airframe and it would prove economic to make, as much of the production equipment would be the same. The outer wing panel and tailplane jigs were the same and the Henley also used the Merlin I engine. Like the Hurricane, and unlike its competitors, the Henley had a fabric-covered frame which would later be proven durable and easy to repair during the Battle of Britain. However, the Henley was to grow up in the shadow of its more successful stablemate and, despite the prototype’s construction beginning in mid-1935, it was always on the back burner because of the Hurricane project. The Henley’s first flight was on 10 March 1937, by which point the RAF had no need for a light bomber, as they felt that the Battle had similar traits and were therefore unwilling to trade like for like. They also preferred for Hawker to concentrate work on the Hurricane project instead. The Henley was converted into a target tug for aerial and anti-aircraft gunnery, and the Merlin engine was tuned down to make it less powerful, which often led it to overheat.
The aircraft that the RAF went to war with in 1939 did not represent the pinnacle of bomber design. The RAF were already placing orders and development schemes for larger and heavier bombers, including the Short Stirling, which was being developed. The prototype flew on 14 May 1939, but was faced with technical delays, and the Luftwaffe’s destruction of its Rochester site in 1940 further delayed deployment until 1941. The four-engined Handley Page Halifax was also under development, with their first test flight being in October 1939 and the Avro Manchester, a fore runner to the iconic Lancaster, first flew on 25 July 1939, with all three of these aircraft marked as replacements for the older Wellington, Whitley, and Hampden bombers. However, war intervened, and problems with the Manchester meant that the older models were continually pressed into service against the Luftwaffe.