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MESSERSCHMITT ME 163 B-1 KOMET
MESSERSCHMITT ME 262 A-1A
The FHC’s rare and unusual Messerschmitt Me 163 Komet was captured by the British at the end of World War II and evaluated by the RAF. It came to the United States from the Imperial War Museum.
Germany created some of the most advanced and unusual weaponry of World War II. The
combination of a heritage of accomplishments in science, engineering, and craftsmanship, and Adolf Hitler’s social and political agenda turned Germany into a war machine.
Hitler’s ambition to “save” Germany included a willingness to fight his European
neighbors on a grand scale. To do so, the people of Germany created sophisticated ships and submarines, top-of-the-line tanks and ground weapons, and some of the most
advanced aircraft the world had ever known.
Perhaps one of the strangest aircraft of the conflict was the Messerschmitt Me 163
Komet. This tailless aircraft was the only operational warplane in history to be powered solely by a rocket engine.
It was designed by Dr. Alexander Lippisch, who had been experimenting with tailless
sailplanes since 1926. The Luftwaffe transferred his group of scientists and engineers to Messerschmitt AG in 1939 in order to develop powered versions of their strange-looking aircraft for experimental and military use. Concurrently, other German scientists,
including Werner von Braun and Hellmuth Walter, were working on rocket engines that
could power aircraft.
The first Me 163, a successor to the DFS 194 powered sailplane, flew for the first time in August 1941 with a Walter RII-203b engine. The plane was fast—faster than any
aircraft in the world in fact—once thundering through the skies at over 620 mph.
Continued refinements to the Me 163 included an even more powerful Walter engine
designated HWK 509, which delivered over 3,700 pounds of thrust. The heart of the plane was this engine, which was fueled by a mixture of T-stoff (hydrogen peroxide and water) and C-stoff (hydrazine hydrate and methyl alcohol). This pair of dangerous chemicals became unthinkably worse when mixed and the plane’s thrust came from harnessing the
violent reaction between them. Beyond the fact that the fuel was corrosive and highly
toxic, mistakes in ground handling or rough treatment of the aircraft during operations could, and often did, result in a massive explosion.
While the engine for the Me 163 was radical, the airframe was even moreso; a set of
swept wings affixed to a rotund fuselage with no horizontal stabilizers. The fuselage was monocoque aluminum with flush rivets. The large wings were plywood, equipped with
flaps, leading edge slots, and elevons—control surfaces that acted as both an elevator and an aileron.
Though unusual, the tailless Me 163 was highly maneuverable and almost impossible
to stall. True to its sailplane heritage, the rocket fighter could be made to sink or spiral, but not plummet from the skies.
In order to make the aircraft as light as possible, it was launched with a main landing gear dolly that was dropped shortly after takeoff. The plane landed using a reinforced skid built into the belly of the fuselage. Pilots had to use extra care to avoid rough landings, which could set off leftover fuels in the plane’s tanks.
Like everything else with this new type of plane, combat tactics had to be modified to maximize the Me 163’s effectiveness. There was insufficient fuel to loiter. Messerschmitt rocket fighters had seven and a half to nine minutes of powered flight time from takeoff to fuel exhaustion.
The Me 163 could launch and climb to attack altitude in two to four minutes. Then, the pilot would approach the enemy bombers from behind and below, or head-on, using his
plane’s superior thrust and speed to make slashing attacks with a pair of 30mm MK 108
cannon. To protect the Me 163 from the defensive fire of the bomber’s machine guns, it was equipped with an armored nosecone and a 90mm-thick bullet-resistant glass
windscreen panel.
While the Komet was noteworthy from a technological point of view, it was less than effective in combat. Hundreds of the planes were built yet they only downed a handful of enemy aircraft over Europe.
The Messerschmitt Me 163 never had the impact in combat that the Luftwaffe hoped
for, due to its limitations. The Luftwaffe was hopelessly outnumbered by thousands of
American aircraft by the time the 163 entered the fighting. Some historians point out that the dangerous rocket plane actually killed more German aviators than American ones
during the last year of war.
The FHC Me 163 carries work number 191660 and was built in late 1944 by Junkers.
When the Messerschmitt factory in Regensburg-Obertraubling was bombed by the Allies,
Komet production was moved. The Germans took the opportunity to switch the factory to production of additional Bf 109 fighters, though repairs took only a few weeks.
This photograph shows the FHC’s Me 163 Komet on display at the Imperial War Museum in 1962. Note that the plane appears to have been repainted since its Luftwaffe service and is missing its blown plastic canopy.
This Komet became a teaching tool and PR attraction at Freeman Field in Indiana. The little rocket plane has lost one wing so that it doesn’t take up as much space in the Army’s hangar. Sections of the plane’s fuselage have been cut away to allow visitors to have a look at the inner workings of the captured aircraft.
Overseeing Komet production then fell to Leichtflugzeugbau Klemm GmbH in Böblingen. Sources report, “The build quality of the Klemm aircraft was much lower than those of the Messerschmitt-built examples. The relative inexperience of the Klemm
company with modern metal aircraft was the main reason. The aircraft were partially built by French slave laborers, who reportedly sabotaged some of the Komets.”
Production management was moved again, this time to Junkers, a company with fewer
projects than Messerschmitt at this late stage in the war. Over time, all production was switched to Junkers. Junkers-built 191660 took to the air for the first time on December 18, 1944, with a short flight from Brandenburg-Briest airfield to Oranienburg, Germany.
The fifty-mile flight took place with the Komet being towed behind a powered plane and then released. Klemm chief test pilot Karl Voy glided the Komet to Junkers facility near Oranienburg for final tests and release to the Luftwaffe. According to the writings of a former Me 163 flyer, Voy and his colleges made at least one powered flight in each
aircraft before it was delivered.
Soon after, the plane was released to Jagdgeschwader 400 and assigned to Gruppe II (II./JG 400) at Brandis, Germany, east of Leipzig. The plane was transported 143 miles to its new location most likely by truck or train. Due to fuel shortages, II./JG 400 had very few engagements with American bombers. It is unclear whether 191660 was ever used in
combat.
In March 1945, the unit was moved to Salzwedel and then to Nordholz in April.
Finally, in May 1945, the unit moved to Husum in northern Germany. It was there that
II./JG 400 surrendered to an RAF regiment on May 8, 1945. The British acquired most of their forty-eight intact Me 163s from this area after searching among the wrecked and
parted out Komets and Me 262s. Komet number 191660 was one of 25 Komets airlifted to the Royal Aircraft Establishment (RAE) in Farnborough. Four others went to the French
Air Force for study.
BIG GUN
When you are hunting big game, you need a big gun. The Messerschmitt Me 163
Komet carried two MK 108 autocannons. Each weapon fired 650 rounds a minute and each explosive round was over one inch in diameter. That is a lot of punching power.
The American .50-caliber aircraft gun was decidedly smaller and lighter.
Making a quick and brutal attack was the only way for a Komet to succeed.
Rocketing along, literally, at over 500 miles per hour, the Me 163 had only minutes of fuel to climb, move into position, and make a pass or two at an Allied bomber
formation before gliding for home. In those rare moments—split seconds, really—
where the hunter and prey were converging at almost 700 miles per hour, a peashooter
was not going to cut it. You needed a knockout blow.
This cutaway drawing, created by the US Army Air Forces, shows the Komet’s pair of bomber-busting guns, buried in the bantam fighter’s thick wings. Each Mk 108 cannon could spit out ten 30mm high-explosive or high-explosive incendiary shells per second. Commonly, a Komet carried sixty rounds, per gun, into combat.
If a ground crewman accidently mixed the chemicals C-stoff and T-stoff, it was most likely the last thing he ever did. As a result, the fillers and drains on the Komet carry clear symbols, distinctive in color, shape, and letter, to keep anyone from inadvertently blowing themselves up, along with the valuable aircraft.
This view of the belly of the Komet reveals the plane’s unusual takeoff and landing equipment. The wheeled dolly under the plane was dropped shortly after takeoff. The ski-like skid, painted dark gray, was extended before landing and the plane would slide to a stop on grass. Also note the cable attachment point just forward of the skid—used to transport the Komet, unfueled, with the help of a piston-powered tow aircraft.
The Komet’s fuselage was bulbous on the outside and cramped on the inside. In an effort to get more fuel in the plane, there isn’t too much room for the pilot. Note the huge, heavy, flat slab of 80-millimeter thick glass up front, designed to stop .50-caliber bullets from American bombers.
Some aircraft have pins in the wings to indicate to the pilot when the landing gear is down. Since the Me 163 has no real landing gear, the red pins in the wings work to let the pilot know when the plane’s flaps have been deployed.
The pint-sized “propeller” at the front of the Komet’s armored nose is actually an impellor. When the fuel from the rocket fighter was used up, these spinning blades provided power to keep the Komet’s electrical system and instruments up and running until the plane touched down for landing.
Simply screwing in fasteners as tight as you can “does not fly” on an operational aircraft. Nuts and bolts are safety-wired into place to keep them from working loose through vibration. These wires appear on the nose of the Komet’s impellor.
This RAE batch of aircraft accounts for many of the Me 163s preserved today in
museums, including Komets at the Science Museum in London, US Air Force Museum in Ohio, Luftwaffe Museum in Berlin, Australian War Memorial in Canberra, and Canada
Aviation Museum in Ottawa.
At the RAE facility, the aircraft were studied thoroughly, so that the technologies could be acquired for future military applications. At least one of the Komets was painted with RAF roundels and fin flash, and made a number of towed flights behind a Spitfire Mk.IX
and glides until it was wrecked during a rough landing in 1947.
The FHC aircraft was assigned code AM 214 and given to the No. 6 Maintenance Unit.
When that RAE unit moved to Brize Norton on July 26, 1945, the aircraft went, too. The aircraft was no longer considered a valuable war prize by September 1946 and was
transferred to the Royal Air Force College, the RAF’s training and education academy, at Cranwell. It was housed in the Station Museum on Cranwell North airfield.
The Me 163 was in this museum until 1961 when it was transferred to the Imperial War
Museum (IWM) for exhibit. Here, it was displayed in the main museum building on
Lambeth Road in London. Rumors are that the original wings were damaged and that parts of other Komets were used to make this plane whole again. It appears in photos from the era with heavily speckled brown and green topsides and the red numeral “3” on the tail.
The emblem of the I./JG 400, Baron von Münchhausen happily riding a flying cannonball, graced the nose. The plane had most definitely been repainted since its German service, either at Cranwell or right after it arrived at the IWM.
Meanwhile, the IWM had been looking for a suitable site for the storage, restoration,
and eventual display of exhibits that were too large for its headquarters in London. The organization obtained permission to use Duxford airfield for this purpose. Cambridgeshire County Council joined with the IWM and the Duxford Aviation Society and, in 1977,
bought the runway to give the abandoned aerodrome a new lease of life.
The Komet was moved to Duxford before, or right after the facility opened. R. L.
Bossom worked on the Komet when it was at Duxford and stated on a Komet website:
“When it arrived from Lambeth it was painted in four-inch paintbrush ‘garden gate green’ and brown and it was in a disheveled state. We were asked by the Director to ‘tart it up’ for display. We had to try and find out as much as possible about 191660 and this proved to be a mammoth task. The markings were not in the correct places, so we had to buy the books by Mano Ziegler and Jeffrey Ethell to try to find out more. The painting [of the Komet took place] over four years.
“We were promised a blown canopy but it never came. The damage to the bulletproof screen appeared in the hangar at Duxford, but I am not sure why. It cannot be proved, but it took a heavy landing at some time since the landing skid was misshapen. It may also have been due to ground handling. The cockpit instrument panel was refurbished in my kitchen, as all the wiring had been cut through from behind this panel after the war, so was easy to remove.
“All the time I worked on it I was amazed at the workmanship and quality of the design of the airframe.”
The FHC’s Me 163 wears a strange symbol on its side—German Baron Münchhausen flying skyward on an uncorked bottle of champagne. In the famous story, notorious tall-tale-teller Münchhausen rides a cannonball, but the symbol of the .7/JG 400
was the Baron atop a hissing bottle of sparkling wine, a fitting emblem considering the Komet’s explosive liquid fuel.
In 1997, the Komet was moved to Duxford’s restoration building—an area open to the public in which aircraft were refurbished by IWM staff and volunteers. During the
restoration, a complete engine, canopy parts, and cannons were installed. The cockpit
remained only partly complete.
Like the Messerschmitt Bf 109, the Me 262 has leading edge slats that automatically deploy at slow speeds. On the ground, you can push the slats upward and aft, and they will fall back into place as soon as you let go. At cruising speed, the air passing over the wing holds the slats in place. When the plane slows, the slats thump down automatically.
In October 1997, Duxford’s Messerschmitt Bf 109 G-2 suffered engine troubles during
an airshow and crash-landed in a field. The plane flipped on its back and suffered major damage. Due to this accident, the spot in the restoration hangar assigned to the Komet was taken over by those working on the Bf 109 wreck.
The Komet was moved to a side building. Periodically, a tourist or enthusiast would sneak behind the museum’s barriers and snap an image of the rocket plane, wings off, in a back corner of the facility. In May 2005, the Komet was loaded on a truck and taken away.
It was soon discovered that the aircraft was sold in order for the IWM to raise the
money it needed to acquire one of two de Havilland D.H.9s found in an elephant stable in India. This aircraft was badly wanted by the museum because D.H.9s operated from
Duxford during World War I. Correspondence between IWM trustees and the FHC date to
late 2003. The FHC purchased the Komet in 2005.
In 2007, Vulcan entered into an agreement with Legend Flyers, based at Paine Field, to restore the Komet. The group was quite familiar with radical German aircraft, being involved in the work of creating five Me 262 replicas for aviation museums. The Kometwent into restoration in November 2007 and was finished in April 2008. The craftsmen at Legend Flyers had assistance from Rudolf Reinhold Opitz, Gruppenkommandeur II./JG
400, on the Luftwaffe markings and nose art.
The newly restored Komet arrived on site before the June 2008 opening of the Paine
Field building, and stands on static display at the southeast end of the hangar.
More impactful on the future of aviation technology than the Me 163 was Messerschmitt’s Me 262 jet fighter. Nearly every modern jet aircraft in the world owes some of its traits, characteristics, and design elements to this iconic fighter aircraft of World War II.
The fighter got its start in 1938 when the German Air Ministry approached
Messerschmitt about making an airframe for new jet engines under development at
Junkers and BMW. Many in the Luftwaffe considered these new engines to be the key to
the next generation of combat aircraft.
However, constant delays and production problems plagued the construction of these
jet engines. BMW and Junkers were forced to redesign their complex power plants many
times. While waiting to get viable engines from BMW, Messerschmitt chose to fly the
aircraft with a piston-powered Jumo 210 engine mounted in the nose.
With unpainted engine inlet cowlings, the FHC’s Me 262 was photographed in France at the end of World War II. The plane still has its original nose in this image, complete with bulges for aerial camera equipment.
The propeller-driven Me 262 took to the skies for the first time in April 1941. Soon,
BMW released early versions of their jet engines to Messerschmitt, but both engines failed during the Me 262’s first jet-powered takeoff in November 1941.
While still waiting for dependable power, Messerschmitt redesigned the plane. After
each failure, it seemed, the promised jet engines got bigger and heavier, and were
predicted to produce less thrust. In order to compensate for more weight and keep the Me 262 suitably balanced, Messerschmitt ordered the outer wings of the aircraft to be swept aft. The rushed design change was purely the simplest solution to a complex problem, but it ultimately helped the fighter’s performance. The swept-back wings helped delay the
onset of high-speed buffeting and compressibility, making the plane capable of high
subsonic speeds.
Luftwaffe test pilots were quite pleased with the radical jet fighter, but Hitler seemed fixated on making the Me 262 a bomber. While Messerschmitt worked to incorporate
conversions to allow the plane fly with a bombsight, additional fuel, and a meager load of explosives, precious months slipped away.
The FHC’s Messerschmitt Me 262 has a storied history; with the Luftwaffe, the US Army Air Forces, and Howard Hughes’s RKO
Pictures. It is now being restored to take to the skies once again.
Shot at an engine shop in California, the first of the Me 262’s Jumo 004 engines takes shape. By using improved metals and modern techniques, engineers hope to get hundreds of hours out of the engines before overhaul.
By mid-1944, after more painful delays caused by German leadership decisions and the
difficulties of producing a sophisticated aircraft with its industry in tatters, Messerschmitt Me 262s began to be built in numbers. Combat versions of the plane flew with Junkers
Jumo 004 jet engines, instead of those from BMW, producing over 1,900 pounds of thrust each.
Despite compromises with engines and airframe, the Me 262 was an amazing aircraft—
able to outpace the Allied fighters by 120 mph or more. The four 30mm MK 108s cannon
in its nose made it deadly when attacking American heavy bombers.
Though the airframe of the Me 262 was fairly conventional, the Jumo 004 jet engines
made the plane tricky to fly. The Jumos were far from perfect, though better than the early BMW engines. A pilot had to use great care, because quick throttle movements could
cause compressor stalls. While a stall was something a flyer could recover from, too much power too quickly would burn out critical components housed in the “hot section” of the engine, destroying the Jumo 004 in flight.
The Jumo engine compressor blade wheels were made with weaker metals, prone to
failure, because many high-quality metals were going to the production of German
submarines. Other parts of the power plant, exposed to great heat, should have been made of high-quality metals but were instead made from mild steel parts coated aluminum. As a result, the life of a Jumo 004 engine in combat was less than twenty-five hours.
Ultimately, it was Germany’s dire situation that doomed the Messerschmitt Me 262.
With weak parts, a shortage of fuel, and very few surviving experienced pilots, it did not matter that the Me 262 was a superior plane. Great numbers of conventional Allied aircraft were attacking Germany daily, and a handful of amazing Me 262 jet fighters piloted by a dwindling group of brave fighter pilots could do nothing to stop the decimation of
Germany.
According to one source, the FHC Me 262 took to the air on March 14, 1945, with
Messerschmitt factory pilot Otto Kaiser at the controls. This was at a flight test facility in Memmingen, Germany. Given the location of the flight, Leipheim and Burgau were the
likely locations for the plane’s final assembly in early March.
Very little is known about the Luftwaffe service history of this Me 262. American
soldiers found the aircraft at an airfield near Lechfeld, south of Augsburg, Germany. The plane was found and photographed in A-1a/U3 configuration, meaning the plane had
different nose hardware than the standard fighter-type Me 262. The 30mm guns were
replaced with a pair of R6-50/30 vertical cameras in the nose compartment.
The large film boxes for the cameras protruded past the streamlined form of the
nosecone necessitating the addition of two distinctive blisters on either side of the front of the aircraft nose. This U3 configuration modification was often completed during the war by Lufthansa at Eger-Cheb, Czechoslovakia.
At Lechfeld, the plane came under the jurisdiction of the 54th Air Disarmament
Squadron (ADS) of the US Army. The German crosses on the sides of the plane were
painted over with US insignia. The swastika at the tail was also painted over. The Me 262
received the moniker Connie the Sharp Article, inspired by the name of the wife of ADS
Master Sgt. H. L. Preston.
Later, as the plane was being prepared for ferrying to a port France, it was renamed
Pick II by its adopted pilot, Lt. Roy Brown of the 86th Fighter Group. Brown’s P-47, Pick, had been named after his wife whose maiden name was Pickrell. The Me 262 was also
assigned the number 444 by the Air Technical Intelligence group.
The planes were flown from Lechfeld to the port of Cherbourg, France. By July 19,
1945, the Me 262 and forty other aircraft, including the FHC Fw 190 D-13, were loaded
aboard the British escort carrier HMS Reaper.
At a port near Newark, New Jersey, the group of aircraft was divided. Some went to the navy, while others were bound for the army’s Wright Field in Ohio. Still others, under the army’s jurisdiction, were diverted to Freeman Field in Seymour, Indiana, “when the field (Wright) could no longer handle additional aircraft.” Colonel Harold E. Watson, the leader of the “Watson’s Whizzers” evaluation group, flew Pick II accompanied by another 262
flown by a pilot named Jim Holt. Both pilots experienced difficulties with the brakes on their jets during a fuel stop in Pittsburg. Watson managed to stop Pick II, while Holt’s aircraft crashed off the end of the runway. The other Me 262 was destroyed, but Holt
walked away from the crash. Soon after, Watson piloted Pick II to Freeman Field. There, the plane was assigned the designator “FE-4012.” At Freeman, the Me 262 was equipped
with a fighter-style nose from another Me 262, designated FE-111. The latter plane is
today on display at the Smithsonian National Air and Space Museum in Washington, D.C.
A milestone in the restoration of the FHC’s Me 262 took place when its one-piece wing was joined to the jet fighter’s fuselage.
The wing is held in place by four large bolts. When the plane is taken to an isolated airfield for test flights, crews will have to disassemble the body and wings once again.
The big gun bay of the Me 262 carried four Mk 108 30mm cannon. Eventually, demilitarized examples of the guns will be installed in the nose as the heavy cannon are critical to the weight and balance of the flying aircraft.
The Messerschmitt Me 262 has a shark-like appearance when viewed from the front. The flat lower fuselage acted as a lifting body for the heavy jet fighter. The lens in the very tip of the Messerschmitt’s long nose is for the plane’s gun camera.
This image shows the half-built cockpit of the FHC’s Messerschmitt Me 262. It was here that Colonel Watson, of “Watson’s Whizzers” fame, sat as he flew this aircraft to Ohio. Renowned German ace Adolph Galland took a turn in the pilot’s seat when the plane was on display at Planes of Fame. And, most likely, Howard Hughes, too, sat in the cockpit of this famous jet fighter.
An early Allied drawing shows the strange plane, without propellers, that the flyers were encountering over Europe. The artist got most of the traits of the Me 262 right, though out of habit perhaps, he could not help but depict the plane with almost completely straight wings.
Replacing the plane’s thick glass windscreen was a challenge for restorers. The unit is almost three inches thick, and yet nearly distortion free. The plane’s gunsight can be rotated clockwise and pushed forward to get it out of the way when not in use.
FE-4012, the FHC aircraft, was reconditioned at Freeman Field and given an overall
smooth finish for performance comparison testing with the American Lockheed P-80
Shooting Star jet fighter. On about May 17, 1946, Watson flew the aircraft to Patterson Field for the start of this series of trials. It was flown at Patterson and Wright Fields on test work for four hours and forty minutes spread over eight flights. Flight trials were
discontinued in August 1946 after four engine changes were required during the course of the tests culminating in two single-engine landings.
Now, no longer of use to the army, it was handed over to the Hughes Aircraft Company
of Culver City, California. It is rumored that Howard Hughes himself was interested in the aircraft for more than technical study. Many sources state that Hughes intended to enter the aircraft in the post-war Thompson Trophy air race, but top generals are said to have
“discouraged” Hughes. The US military was going to enter a P-80 Shooting Star jet fighter in the race and it would make for bad press should a German design win the high-speed
dash instead of the hometown, or homeland, favorite. The plane’s engines were run at the Culver City plant, but it was never flown. About this time, the FE-4012 number was
changed to T2-4012.
RKO Pictures, a Hughes-controlled movie studio, asked to use the jet as a prop in a
film in 1949. The air force agreed and the plane was transported from the Hughes Aircraft Company to an RKO lot. The plane remained with the studio for two years and appeared
in early versions of the John Wayne film that would become Jet Pilot some eight years later.
RKO attempted to return 4012 to the air force in 1951, but it was no longer wanted.
Since donation was easier than scrapping the plane, it was given to Glendale Aeronautical School for use by students as an instructional airframe.
Edward T. Maloney acquired the plane, now in fairly rough shape, in approximately
1955 for his Planes of Fame Air Museum, then at Claremont, California. The plane stayed in the museum collection for many years and underwent one or more restorations. It was marked in a “White Nine” color scheme copied from another long lost 262.
In 2000, the FHC purchased the Me 262 and another aircraft from Edward Maloney.
The restoration of this rare airframe was taken on by a number of companies—JME
Aviation Ltd. in England, GossHawk Unlimited Inc. in Arizona, and Morgan Aircraft
Restorations in Washington.
Aero Turbine Inc. in California tackled perhaps the most challenging part of the
restoration. Two wartime Jumo 004 jet engines are currently being rebuilt using modern metals in critical spots to extend the life of the engines to several hundred hours of flight time.
When the Me 262 flies for the first time since World War II, it will be the only original, flying Messerschmitt Me 262 in the world.
American soldiers swarm over an abandoned Me 262 they found hidden among the trees near the front lines. In the last months of the war, German aviation units often dispersed their planes in the woods, flying from sections of the Autobahn to avoid Allied fighter bombers prowling the German airfields.
The FHC’s Messerschmitt, smoothed for speed tests, was photographed at Wright Field during evaluations. Tests on the plane ceased after a series of engine failures similar to those experienced while the Me 262 jet fighter was used in combat by the Germans.
The fuel tank access doors on the belly of the aircraft are made from a primitive sort of honeycomb structure. The spot-welded steel grid is sandwiched between two steel sheets. Built near the end of the war, the Germans were often forced to use steel in the place of lighter aluminum alloys.