The Messerschmitt Me 262 was the first operational jet fighter in the world. Its Jumo 004 turbojet powerplants and swept wing made it one of the most extraordinary designs of World War II. The Me 262A-1a achieved an incredible top speed for its time of 870 km/h (497 mph) at an altitude of 6000 meters (19,685 feet), nearly 200 km/h faster than the North American P-51 Mustang. The Me 262 also employed the deathly firepower of four nose- mounted MK-1 08 30 mm cannon. Its operational service, however, was hampered by the unreliability of its engines and its weak undercarriage.
The first serial-produced Me 262A-1a (Werknummer 1300061VI+AF) took off on its maiden flight on 28 March 1944. The first Me 262s were allocated to Erprobungskommando 262, a special fighter evaluation unit of the Luftwaffe under the command of Hauptmann (Captain) Werner Thierfelder, on 19 April 1944 at Lechfeld airfield in Bavaria.
Leutnant (Lieutenant) Alfred Schreiber scored the first victory with the Me 262, and the first victory ever of a jet-powered fighter, when he shot down a Mosquito on 26 July 1944. The Blitzbomber (literally "lightning bomber") version received the designation Me 262A-2a. The Me 262A-2a had the upper two MK-108 cannons removed and a pair of ETC 503 Wikingerschijf ("Viking ship") bomb racks mounted on the nose undersurface. The Me 262A-2a could carry either two SC-250 blast bombs or two SD-250 fragmentation bombs.
A total of 1,433 Me 262s were built, assembled at Leipheim (Kuno I and Kuno IT), Schwabisch Hall-Hessental, Obertraubling near Regensburg, Neuburg/Donau-Bruck, Eger, Kahla, and Brandenburg-Bliest. Messerschrnitt AG made wide use of concentration camp prisoners and forced labor supplied by the Waffen SS-owned Deutsche Erd- und Steinwerke GmbH (German Earth and Stone Works Company) to keep Me 262 production at a rapid pace. Nearly 53,000 prisoners and forced laborers were employed in the manufacture of parts, components, and final assembly.
Czechoslovakia became the only other country in the world to use the Messerschmitt jet fighter operationally. The Avia company at Cakovice began building the Me 262 from components left behind in the country after the end of World War II. The type received the designation S-92. A total of seven S-92 and three CS-92 trainers were built, the last S- 92 being accepted on 24 September 1948. The S-92 became a training aircraft in 1949. Most S-92s and CS-92s were phased out of service after 1951 and subsequently scrapped.
The jet propelled Me 262 introduced in the last year of the war was 100 mph faster than contemporary piston-engine fighters and well armed with four 30mm cannons.  In a head-on attack, its 350 yards per second closing rate was too fast to allow accurate aiming or to allow optimum use of its short-ranged armament. To overcome this, German Jet pilots used the "roller coaster" attack. Approaching from astern at about 6000 ft above the bombers, the jets pushed over into a shallow dive starting about 3 miles away. They quickly built up speed such that the escorts could not follow them. Diving down until they were about a mile behind and 1500 ft below, they pulled up sharply to bleed off speed, leveling off at 1000 yds astern in position to deliver an attack.
Later in the war, the Germans introduced the Mk 108 30mm heavy cannon capable of firing 600 11-ounce high explosive rounds per minute. Three hits with this weapon were usually sufficient to bring down a Flying Fortress. On the other hand it was a low velocity weapon and its effective range was shorter than the 20-mm cannon forcing German pilots to fly even closer to get hits.
"I passed one that looked as if it was hanging motionless in the air (I am too fast!). The one above me went into a steep right-hand turn, his pale blue underside standing out against the purple sky. Another banked right in front of the Me's nose. Violent jolt as I flew through his airscrew eddies. Maybe a wing's length away. That one in the gentle left-hand curve! Swing her round. I was coming from underneath, eye glued to the sight (pull her tighter!). A throbbing in the wings as my cannon pounded briefly. Missed him. Way behind his tail. It was exasperating. I would never be able to shoot one down like this. They were like a sack of fleas. A prick of doubt: is this really such a good fighter? Could one in fact, successfully attack a group of erratically banking fighters with the Me 262?"
Johannes Steinhoff, Luftwaffe fighter ace.
The Junkers Jumo 004 was the world's first turbojet engine in production and operational use, and the first successful axial compressor jet engine ever built. Some 8,000 units were manufactured by Junkers in Germany during late World War II, powering the operational Messerschmitt Me 262 fighter jet and the Arado Ar 234 reconnaissance / bomber jet, along with prototypes including the Horten Ho 229 aircraft. Variants of the engine were produced in Eastern Europe for years following the war.
The first prototype 004A, which was constructed to run on diesel fuel, was first tested in October 1940, though without an exhaust nozzle. It was benchtested at the end of January 1941 to a top thrust of 430 kgf (4,200 N; 950 lbf), and work continued to increase the output, the RLM contract having set a minimum of 600 kgf (5,900 N; 1,300 lbf) thrust.
Vibration problems with the compressor stators, originally cantileverd from the outside, delayed the program at this point. Max Bentele, as an Air Ministry consulting engineer with a background in turbocharger vibrations, assisted in solving the problem. The original aluminium stators were replaced with steel ones in which configuration the engine developed 5.9 kN (1,300 lbf) in August, and passed a 10-hour endurance run at 9.8 kN (2,200 lbf) in December. The first flight test took place on March 15, 1942, when a 004A was carried aloft by a Messerschmitt Bf 110 to run up the engine in flight. The 004 used an eight-stage axial-flow compressor, with a number of axial combustion chambers (made from sheet steel), and a one-stage turbine with hollow blades.
On July 18, one of the prototype Messerschmitt Me 262s flew for the first time under jet power from its 004 engines, and the 004 was ordered into production by the RLM to the extent of 80 engines.
The initial 004A engines built to power the Me 262 prototypes had been built without restrictions on materials, and they used scarce raw materials such as nickel, cobalt, and molybdenum in quantities which were unacceptable in production. Franz realized that the Jumo 004 would have to be redesigned to incorporate a minimum of these strategic materials, and this was accomplished. All the hot metal parts, including the combustion chamber, were changed to mild steel protected by an aluminum coating, and the hollow turbine blades were produced from folded and welded Cromadur alloy (12% chromium, 18% manganese, and 70% iron) developed by Krupp, and cooled by compressed air "bled" from the compressor. The engine's operational lifespan was shortened, but on the plus side it became easier to construct. Production engines had a cast magnesium casing in two halves, one with half-sections of stator assemblies bolted to it. The four front stators were constructed from steel alloy blades welded to the mount; the rear five were pressed steel sheet bent over the mount and welded on. Steel alloy compressor blades dovetailled into slots in the compressor disk and were fixed by small screws. The compressor itself was mounted to a steel shaft with twelve set screws. Jumo tried a variety of attach compressor blades, beginning with solid steel, later hollow sheet metal ones, welded on the taper, with their roots fitted over rhomboidal studs on the turbine wheel, to which they were pinned and brazed.
The first production model of the 004B weighed 100 kg (220 lb) less than the 004A, and in 1943 had passed several 100 hour tests, with a time between overhauls of 50 hours being achieved.
Later in 1943 the 004B version suffered turbine blade failures which were not understood by the Junkers team. They focused on areas such as material defects, grain size and surface roughness. Eventually, in December, blade-vibration specialist Max Bentele was once again brought in during a meeting at the RLM headquarters. He identified that the failures were caused by one of the blades` natural fraquencies being in the engine running range. His solution was to raise the frequency, by increasing the blade taper and shortening them by 1 millimeter, and to reduce the operating speed of the engine from 9,000 to 8,700 rpm.
It was not until early 1944 that full production could finally begin. These setbacks were the principal factor delaying the Luftwaffe's introduction of the Me 262 into squadron service.
Given the lower-quality steels used in the 004B, these engines typically only had a service life of some 10–25 hours, perhaps twice this in the hands of a skilled pilot. Another shortcoming of the engine, common to all early turbojets, was its sluggish throttle response. Worse, it was fairly easy to inject too much fuel into the engine by throttling up too quickly, allowing heat to build up before the cooling air could remove it. This led to softening of the turbine blades, and was a major cause for engine failures. Nevertheless, it made jet power for combat aircraft a reality for the first time.
The exhaust area of the 004 featured a variable geometry nozzle, which had a special restrictive body nicknamed the Zwiebel (German for onion, due to its shape when seen from the side) which had roughly 40 cm (16 inch) of fore-and-aft travel to vary the jet exhaust's cross-sectional area for thrust control, as the active part of a pioneering "divergent-convergent" nozzle format.
One interesting feature of the 004 was the starter system, which consisted of a Riedel 10 hp (7.5 kW) 2-stroke motorcycle engine hidden in the intake, and essentially functioned as a pioneering example of an APU for starting a jet engine. A hole in the extreme nose of the intake diverter body contained a pull-handle for the cable which "turned-over" the piston engine, which in turn spun up the turbine. Two small gasoline/oil mix tanks were fitted within the upper perimeter of the annular intake's sheet metal housing for fueling the Riedel two-stroke mechanical APU unit.
The Jumo 004 could run on three types of fuel:
J-2, its standard fuel, a synthetic fuel produced from coal.
Aviation gasoline; not considered desirable due to its high rate of consumption.
Costing RM10,000 for materials, the Jumo 004 also proved somewhat cheaper than the competing BMW 003, which was RM12,000, and cheaper than the Junkers 213 piston engine, which was RM35,000. Moreover, the jets used lower-skill labor and needed only 375 hours to complete (including manufacture, assembly, and shipping), compared to 1,400 for the BMW 801.
Production and maintenance of the 004 was done at the Junkers works at Magdeburg, under the supervision of Otto Hartkopf. Completed engines earned a reputation for unreliability; the time between major overhauls (not technically a TBO) was thirty to fifty hours, and may have been as low as ten, though a skilled flyer could double the interval. (The competing BMW 003's was about fifty.) The process involved replacing turbine blades (which suffered the most damage, usually from ingesting stones and such, later known as fodding) and rebalancing the rotors; the starter and governor would also be examined and replaced as needed. Combustors required maintenance every twenty hours, and replacement at 200.
Between 5,000 and 8,000 004s were built; at the end of the Second World War, production stood at 1,500 per month. The Fedden Mission, led by Sir Roy Fedden, postwar estimated total jet engine production by mid-1946 could have reached 100,000 units a year, or more.