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As the Second World War in Europe drew to a close, a powerful new twin-
engined fighter was preparing to enter service with the Luftwaffe. The
unique configuration of this aircraft conferred on it a phenomenal
performance, which completely eclipsed all of its contemporaries; whilst
its potential for devastating the massive Allied bomber streams that almost
daily pounded the Reich was rivalled only by the Me262 jet. This amazing
machine was the piston-engined Dornier Do335.
Aircraft designers are constantly seeking to maximize engine power and
minimize drag. The increased power resulting from the adoption of a twin-
engined layout, is normally partially offset by the increased drag and
reduced manoeuvrability of an orthodox wing-mounted arrangement. An
alternative arrangement, with the two engines mounted fore-and-aft in
tandem is known as centre-line thrust. With the power from both engines
being delivered along the aircraft centre-line, the obvious benefits of
this layout include reduced frontal area, an aerodynamically clean wing and
the elimination of the asymmetry problems associated with engine failure.
The Dornier Do335 was a bold attempt to embody the centre-line thrust
concept in a practical and efficient airframe. Its unique layout featured
a conventional nose mounted engine and tractor airscrew, together with a
second engine located in the rear fuselage, driving a pusher propeller
situated aft of the tail unit.
The origins of the Dornier Do335's novel layout go back to the First World
War. During the war Prof. Claude Dornier designed a number of flying
boats, which typically featured a tandem engine installation. The engines
were mounted back-to-back in pairs, with the forward unit driving a tractor
airscrew and the aft facing unit a pusher propeller. This engine
arrangement was subsequently adopted for the highly successful Dornier DoJ
Wal (Whale) flying boat of 1922.
In 1935 Dornier produced the Do18, a much improved development of the Wal
concept. To enable the pusher propeller to clear the trailing edge of the
broad chord wing featured on this type, an extension drive shaft from the
rear engine was introduced for the first time. The idea of placing the
pilot between the two engines in such an arrangement obviously occurred to
Dornier. Indeed, on 3rd August 1937 he filed patent number 728044 for an
aircraft of just such a configuration. It was on the basis of this patent
that the Do335 came to be developed.
During 1939 Dornier was busy working on the P.59 high speed bomber project,
which featured the tandem engine layout patented earlier. Work on the P.59
was stopped in early 1940 when Reichsmarschall Goering, anticipating a quick
end to the war, ordered the cancellation of all work which would not see
fruition within a year or so.
Despite this setback, Dornier soon began working on another unarmed high
speed bomber project - the P.231. With an internal bomb load of 2200 lb,
this design used a similar configuration to that of the P.59. In May 1942
Dornier submitted a refined version of the P.231 design in response to a
Technische Amt requirement for a single seat high speed bomber. The
Dornier proposal was selected as the winner after beating rival designs
from Arado and Junkers. Despite official resistance to the unconventional
layout,a development contract was awarded under the RLM designation Do335.
In the Autumn of 1942, with detail design progressing, Dornier were
informed by the RLM that the Do335 was no longer required. In the light
of the massive Allied air raids which had begun that year, the aircraft was
to be redesigned as a multi-role fighter of broadly similar performance.
Capable of duties as a single-seat fighter bomber, high speed
reconnaissance, heavy fighter, and two seat night and all-weather
interceptor.
However, the Technische Amt delayed issuing a formal contract, and Dornier
eventually turned to the Inspector-General of the Luftwaffe,
Generalfeldmarschall Milch, to expedite matters. The necessary redesign had
been completed, and the first metal cut on the prototypes at
Oberpfaffenhofen by the end of 1942.
As construction of the prototypes proceeded, the war situation was growing
more serious. On 7 June 1943, Hitler himself intervened to expedite the
Do335 and Me262 programmes. However, on 7 Sept 1943 Messerschmitt
persuaded Hitler that the Me262 would be a better suited as a high speed
bomber than the Ar234 or Do335, and the Me262 received sole priority. This
was despite the fact that the Do335's bomb load was twice that of the
Me262. Milch's advocacy of the other two types was brushed aside.
Fitted with Daimler-Benz DB603A-2 engines delivering 1750 hp at take-off,
the first example, Do335 V1 (CP+UA), flew for the first time on 26 October
1943 from Mengen, Wurttemburg, with Flugkapitan Hans Dieterle at the
controls.
Aside from its unusual engine layout, the design incorporated several other
unusual features. These included a reversible-pitch tractor airscrew, to
shorten the rather long landing run; a wing leading edge de-icing system;
hydraulically operated flaps; a tunnel radiator for the rear engine and a
compressed air powered ejection seat. The latter being essential for a
safe bale-out clear of the rear propeller, although the vertical tail and
propeller could be jettisoned by explosive bolts when required.
After initial handling trials at Oberpfaffenhofen, the Do335 V1 was ferried
to the Rechlin Erprobungstelle for official evaluation. Although some
snaking and porpoising was found at high speeds, the Rechlin test pilots
were generally enthusiastic. They commented favourably on its general
handling behaviour, manoeuvrability and in particular on its acceleration
and turning circle. However, they also criticized the very poor rearward
vision and weak undercarriage.
During the Winter and Spring of 1943-44, the first prototype was joined on
the test programme by additional development aircraft. The Do335 V2
(CP+UB) and V3 (CP+UC/T9+ZH) incorporated several minor changes with
respect to the first prototype. The oil cooler intake under the nose was
deleted and incorporated into an enlarged annular engine cowling; blisters
were added to the cockpit canopy to house small rear view mirrors, and the
main undercarriage doors were redesigned. Both aircraft were retained at
Oberpfaffenhofen for further flight trails.
The Do335 V4 was intended to be the prototype for the two-seat Do435 night
and all-weather interceptor, featuring side-by-side seating, cabin
pressurisation, 2500 hp Jumo 222 engines and long span wooden outer wing
panels. It was cancelled by the RLM in the Autumn of 1944 whilst still
under construction.
The Do335 V5 (CP+UE) was the armament test prototype, fitted with a 30 mm
engine mounted MK103 cannon, and two 15 mm MG151 cannon mounted in the
upper nose. The Do335 V6 (CP+UF) and V7 (CP+UG) were retained at
Oberpfaffenhofen for various equipment trials. The V7 later being
transferred to Junkers at Dessau for ground tests with Jumo 213 engines
installed. The Do335 V8 (CP+UH) was used as an engine test bed, by
Daimler-Benz.
The main production line was intended to be at Manzel, but a bombing raid
in March 1944 destroyed much of the production tooling and forced Dornier
to set up a new line at Oberpfaffenhofen.
On 23 May 1944, with an Allied invasion of France expected at any time,
Hitler ordered maximum priority to be given to the Do335 production effort.
The decision was made to cancel the Heinkel He219, and use its production
facilities for the Do335. However, Ernst Heinkel resisted the
cancellation, and managed to delay (and eventually ignore) its
implementation.
The Do335 V9 (CP+UI) was the prototype for the Do335A-0 pre-production
model. Fitted with a strengthened undercarriage, DB603A-2 engines, and
full armament, it was delivered to the Rechlin Erprobungstelle in May 1944
for further official trials. It was shortly followed off the
Oberpfaffenhofen production line by the first Do335A-0 (VG+PG). In all,
ten Do335A-0 fighter-bombers were produced. Several were used by
Erprobungskommando 335 (EK335), formed in September 1944 for the service
evaluation and development of operational tactics for this new type.
In late 1944, the Do335A-1 superseded the A-0 on the production line. This
was the initial production model, similar to the A-0 but with the uprated
DB603E-1 engines and two underwing hard points for additional bombs or drop
tanks. Delivery commenced in January 1945.
Capable of a maximum speed of 474 mph at 21,325 ft with MW 50 boost, or 426
mph without boost, and able to climb to 26,250 ft in only 14.5 minutes, the
Do335A-1 could easily outpace any Allied fighters it encountered. It could
also carry a bomb load of 1100 lb for 900 miles.
Although given the nickname 'Pfeil' (arrow) by Dornier test pilots, on
account of its speed, service pilots quickly dubbed it 'Ameisenbaer' (ant-
eater) because of its long nose.
The Do335A-2 And A-3 were proposed developments with improved cannon
armament, but were never built. One Do335A-0 became the prototype for the
Do335A-4. This was an unarmed long range reconnaissance model, with two
Rb50/30 cameras in the weapons bay and DB603G engines. Ten A-4s were
ordered for production, but none were completed.
The Do335 V10 (CP+UK) was the prototype for the Do335A-6 radar equipped
two-seat night fighter variant. A second cockpit for the radar operator
was inserted above and behind the normal cockpit. The weapons bay was
replaced by a redesigned fuel tank, radar antennae were attached to the
wing leading edges and flame dampers fitted to the exhausts. However, the
FuG217 radar equipment was never actually fitted to the V10. Production
of the A-6 was transferred to Heinkel in Vienna, but none were assembled.
The Do335 V11 (CP+UL) and V12 (CP+UM) were prototypes for the Do335A-10 and
A-12 dual control conversion trainers respectively. The former having
DB603A engines and the latter DB603E powerplants. The instructor occupied
the second cockpit - although without an ejection seat, due to production
shortages. Production examples were interspersed with the A-1 on the same
production line.
As the war situation continued to deteriorate, development effort switched
from the A-series fighter-bomber to the more heavily armed B-series heavy
fighter. The Do335 V13 (RP+UA) was the prototype of the Do335B-1 which
featured a revised nose undercarriage arrangement - the larger wheel being
tilted at 45 degrees when fully retracted, a V-shaped armoured windscreen
and DB603E engines. It's weapons bay was replaced by an additional fuel
tank, and the two 15 mm MG151 cannon in the nose replaced by 20 mm MG151s.
The B-4 prototype, Do335 V14 (RP+UB) had this armament supplemented by two
30 mm MK103 cannon mounted on the inner wing leading edges. Only the two
B-series prototypes were actually completed and flown - further
developments were still under construction, some with two-stage
supercharger DB603LA engines capable of 2100 hp.
Plagued by mechanical unreliability and lack of aviation fuel, the
operational career of the Do335 is rather obscure. Do335A-0 and A-1
aircraft are thought to have flown a number of operational missions with
EK335. Some were also used by III/KG2 in the Spring of 1945. There is no
evidence of the type being met in combat, so it seems likely that all the
operations were high speed interdiction missions - many taking place at
night.
When the US Army overran the Oberpfaffenhofen factory in late April 1945,
only 11 Do335A-1 single seat fighter-bombers and two Do335A-12 conversion
trainers had been completed. A further nine A-1's, four A-4's and two A-
12's were in final assembly, and components and assemblies for nearly 70
more had been completed. Heinkel at Vienna had been unable to build any
Do335A-6 night fighters.
A number of planned developments of the Do335 were on the drawing board
when the war ended, including several big-winged high altitude fighter
versions, the Do535 with a jet rear engine, the Do635 (later Ju 8-635) long
range reconnaissance version which featured twin fuselages linked by a
common wing centre section, and the P.256 twin jet fighter.
As part of Operation Seahorse, two of the surviving A-0 single seaters were
put aboard the US aircraft carrier 'Reaper' and shipped back to the USA,
for detailed evaluation by the US Navy. The two airworthy A-12 two seaters
were flown to Britain and flight tested at RAE Farnborough. Both were
destroyed in crashes. Two of the B-series prototypes were also evaluated
by the CEV in France.
Today, the sole remaining example of this unique type is on display at the
National Air and Space Museum in Washington DC. Do335A-0 VP+GH (Wk Nr.
240102) was one of the two examples evaluated at the US Navy's Patuxent
River Test Center in 1945. Thereafter, it languished in open storage for
27 years in the grounds of the NASM storage facility at Silver Hill. In
October 1974 the decaying airframe was flown back to Munich, for a complete
restoration by Dornier Aircraft at Oberpfaffenhofen (then building
Alphajets). The magnificently restored aircraft was first displayed at the
Hannover Airshow, 1 – 9 May 1976, and then loaned to the Deutches Museum,
Munich, for a several years before returning to the NASM.
Technically innovative, heavily armed, and possessing a performance which
no other piston-engined aircraft has ever achieved or surpassed, the Do335
possessed great potential as a combat aircraft, but never got the chance
to prove itself. Delayed by high ranking indecision and Allied bombing
raids, it simply ran out of time.
