A heavy fighter is a historic category of fighter aircraft produced in the 1930s and 1940s, designed to carry heavier weapons or operate at longer ranges than light fighter aircraft. To achieve performance, most heavy fighters were twin-engined, and many had multi-place crews; this was in contrast to light fighters, which were typically single-engined and single-crew aircraft. In Germany, these larger fighters were known as Zerstörer ("destroyers").
The heavy fighter was a major design class during the pre-World War II period, conceived as long-range escort fighters or heavily armed bomber destroyers. Most such designs failed in this mission, as they could not maneuver quickly enough against single-engine fighters. Most notable among such designs was the Messerschmitt Bf 110, which suffered great losses during the Battle of Britain. An exception was the American Lockheed P-38 Lightning, which proved an effective heavy fighter; even against smaller, lighter, single-engine aircraft and particularly in the Pacific theater.
Many twin-engine heavy fighters found their niche as night fighters, especially in the bomber-destroyer role; or as fighter-bombers, roughly analogous to modern strike fighters. Among such conversions was the Bf 110, which served as a relatively successful night fighter, ground attacker, and fighter-bomber for most of the war; and the Bristol Beaufighter, which emerged as a major anti-shipping strike fighter of the Royal Air Force. Some heavy fighters did find success; the de Havilland Mosquito, simultaneously developed as a light bomber, twin-engine fighter and photo-reconnaissance aircraft, excelled in its originally proposed role as a fast light bomber.
Although not always contemporaneously referred to explicitly as “heavy fighters,” nearly every single combatant of WWII fielded or experimented with twin-engine multi-role combat aircraft.
Netherlands
The Fokker G.I was a private venture design by Dutch aircraft manufacturer Fokker in 1936. The G.I was designed to serve on the heavier end of the spectrum of heavy fighters, as a jachtkruiser or a bomber destroyer, and was comparable to early models of the German Messerschmitt Bf 110. The G.I was formidably armed relative even to other early heavy fighters; with twin 23 mm (.91 in) Madsen cannons, and a pair of 7.9 mm (.31 in) Madsen machine guns (later up-armed to eight machine guns) in the nose. For defensive purposes, a single Madsen 7.9 mm machine gun was mounted in a rear-facing turret, manned by the second crew-member.
Prior to the Nazi German invasion of the Netherlands, the G.I was actively involved in air-border patrols in order to ensure neutrality and the integrity of Dutch airspace. On 20 March 1940, a G.I forced down an Armstrong Whitworth Whitley from No. 77 Squadron RAF when it strayed into Dutch air space.
On 10 May 1940, when Nazi Germany invaded, 23 G.I aircraft were serviceable. In the "Five-day War", the available G.I fighters were mainly deployed in ground attack missions, strafing advancing German infantry units, but were also used to attack Junkers Ju 52 transports. Although reports are fragmentary and inaccurate as to the results, G.I fighters were employed over Rotterdam and the Hague, contributing to the loss of 167 Ju 52s, scoring up to 14 confirmed aerial kills. With relentless attacks by the Luftwaffe on Dutch airfields, and overwhelming German air superiority, the G.I suffered heavy losses.
At the conclusion of hostilities, several G.Is were captured by the Germans, and utilized as heavy-fighter trainers for Bf 110 crews at Wiener Neustadt. For the next two years, Flugzeugführerschule (B) 8 flew the G.I until attrition grounded the fleet. On 5 May 1941, a Fokker test pilot, Hidde Leegstra, accompanied by engineer (and member of the Fokker Board of Directors) Dr. Piet Vos, managed to fly a G.I to England from the occupied Netherlands. After landing in England, the G.I was conscripted by Phillips and Powis Aircraft. The company had designed an all-wooden fighter-bomber, and was interested in the G.I wing structure and its resistance to the rigours of a British climate. Despite being left outdoors for the remainder of the war, the G.I survived only to be eventually scrapped after 1945.
There are no surviving G.Is today, although a replica has been built, and is now displayed at the Dutch Nationaal Militair Museum (National Military Museum).
France
In 1934, the French Ministry of Air issued a specification for a new two or three-seat multi-role fighter, capable of functioning as a bomber escort and night fighter, as well as providing fighter direction (leading formations of single-engine fighters to their targets). The specification also required, at minimum, two forward-facing 20 mm cannons, as well as a rearward-facing machine gun for defensive purposes. This was relatively very heavy armament for a fighter in 1934, with most contemporary aircraft mounting one or two light machine guns.Danel 1967, p. 4.
In response, French aircraft manufacturer Potez developed the Potez 63 series.Danel 1967, p. 4. The basic design was close to the original specification; that of either a 2 or 3 seat, dual-engine heavy fighter, armed with two 20 mm Hispano-Suiza HS.404 cannons in gondolas under the fuselage and a rearward-facing machine gun for defense. Numerous variants and sub-variants of the 63 series would be designed and produced, including day fighter, night fighter, reconnaissance, and light bomber variants.Danel 1967, p. 4.
While the 63 series was primarily developed for the French Air Force and French Naval Air Arm, they would serve with numerous other nations, both Axis and Allied powers, via either pre-armistice sales by the French government, or via use of captured aircraft.Breffort and Jouineau 2005, p. 67Danel 1967, pp. 4, 6.
In French service the series saw action during the Battle of France, and post-armistice within both the Vichy French Armée de l'air de l'Armistice, and the Free French Forces Aériennes Françaises Libres. On 20 May 1940, the light bomber variant, the Potez 633, took part in a ground attack against German troops near Arras. Three 633s took part in the attack. This was the type's only operational mission over France as two days later the 633 was withdrawn from front-line service.Green 1967, p. 54. The day/night fighter variant, the Potez 631, had quickly proved to be an ineffectual interceptor; it was slower than some German bomber aircraft and slower than the Messerschmitt Bf 109 E-variant fighter. Perhaps the most successful unit operating the Potez 631 was the Flottille F1C of the French Naval Air Arm. Between 10 and 21 May 1940, aircraft of the flottille shot down 12 enemy aircraft in exchange for 8 of their own losses prior to its withdrawal from active combat.Danel 1967, p. 12. The reconnaissance variants, the Potez 637 and 63.11, equipped numerous Groupes de Reconnaissance of the French Air Force, with more than 700 reconnaissance Potez 63.11s having been delivered.Danel 1967, p. 11.
The Potez 63.11 suffered the more losses than any other French type. One factor contributing to the high losses was the near-complete lack of spares, rendering 70 63.11s unserviceable even prior to the German invasion; many aircraft were destroyed on the ground by enemy bombing and strafing attacks, and entire units were wiped out without conducting a single mission.Danel 1967, p. 12.
In addition to the Potez 63 series, another aircraft was developed from the original 1934 heavy fighter specification. This was the Bréguet 690, designed and manufactured originally by Bréguet Aviation. While the Bréguet 690 was not selected to serve as France's primary heavy fighter, the French Air Force's command staff was still intrigued by the sturdy and versatile design. By 1938, with France falling behind in ground-attack/close-air support aircraft, the decision was made by the Air Force to re-designate the Bréguet 690 as the Bréguet 691, and to utilize it as a ground-attack aircraft. The 691's engines proved unreliable in testing, and the decision was made to mount new engines on the design, which was finally designated as the Bréguet 693.
Few 693s were completed before the Nazi German invasion, however, enough were completed to see some action. The 693 made its combat debut on 12 May 1940 when twelve 693s were sent to attack a German mechanized column near Tongeren. Six to eight were shot down by German flak, two more 693s were lost while attempting to return to base, and of those that made it home safely, one was written off (most of the twenty four crewmen survived or were captured alive, although three died during the attack and some of the survivors were badly wounded). As the fighting drew to a close the French attempted to fly as many 693s as possible to North Africa, but only three made the flight, and none were used by the Vichy Air Force in North Africa. In November 1942 with the German occupation of Vichy France, the remaining Bréguets were seized. Some had their engines removed for use in German aircraft, while others were passed on to the Italians, who used them as training aircraft.
Germany
The Messerschmitt Bf 110 was a pre-war German fighter design to meet a RLM specification for a long-ranged fighter. Prior to the war, it was considered by the German Luftwaffe more important than their single-engine fighters. Many of the best pilots were assigned to Bf 110 wings, specifically designated as Zerstörergeschwader ("destroyer squadron", Zerstörer being the same word as used for naval destroyers) wings. While lighter fighters were intended for defense, the destroyers were intended for offensive missions: to escort bombers on missions at long range, then use its superior speed to outrun defending fighters that would be capable of outmaneuvering it.
This doctrine proved to be a costly mistake. In practice the Bf 110 was capable of using this combination of features for only a short time, until the late summer of 1940. It served well against the Hawker Hurricane during the Battle of France, but was easily outperformed by – and up to 50 km/h (31 mph) slower in top speed than – the Supermarine Spitfire during the Battle of Britain. Eventually Bf 110s were converted to interceptors, and were particularly successful in the later marks of the Bf 110G series from 1942 to 1943 onwards as night fighters, serving as the primary aircraft of the Luftwaffe Nachtjagdgeschwader night fighter wings, using various versions of the Lichtenstein radar for nocturnal interception of RAF Bomber Command heavy bombers, as well as finding some use as ground-attack aircraft. The Me 210 and Me 410 Hornisse were all-new aircraft designs meant to replace the Bf 110, but also could not outrun contemporary single-engine fighters, with the Me 210 having serious aerodynamic problems from mistakes in the design of its wing planform and the initial design of its rear fuselage.
Aside from the Bf 110 and Me 210/410, the Luftwaffe also utilized various light bombers, medium bombers, and Schnellbombers (German; literally "fast bomber") in the heavy fighter role. Due to their relatively large size, these were mostly used as night fighter-bomber destroyers, as there was ample room to install airborne intercept radar systems as well as heavy armament. Bombers utilized in such a role included the Junkers Ju 88 and Ju 388; the Heinkel He 219; and the Dornier Do 215 and Do 217.