The Treaty of Versailles that ended the First World War also sought to end German militarism and, with it, the aviation forces that had introduced the civilian populations of France and southern England to indiscriminate aerial bombardment. To this end, all aircraft manufacturing in Germany—whether for civil or military purposes—was banned in the short term, all existing airplanes were ordered confiscated or destroyed, and military aviation was expressly forbidden to Germany forever. The military junta that in effect ruled Germany from 1917 until the rise of Hitler was, however, undeterred by either the Allied injunctions or the horrendous evidence of its own folly—the shattered economy, the starving and rebellious population, the lost territory, and the generation of dead and mutilated young men that militarism had consumed. Having at last learned the military value of aviation, the generals were determined to possess this weapon once more, if only in secret. When the initial subterfuges—Polizeiflieger ("police" aviation units) and transparently paramilitary airlines—failed to fool the Allied Control Commission, Germany's high command set out on an aggressive program of extraterritorial rearmament. This campaign reached its zenith at an unlikely secret air base in the Soviet Union: Lipetsk.
The scope of Germany's foreign military, naval, and aeronautical ventures is breathtaking in its audacity, even after almost 80 years. Within months of the Great War's conclusion, major arms manufacturers had established foreign subsidiaries to carry on thinly disguised German research, development, and production. Switzerland, Sweden, Lithuania, and Finland supplied cover for continued gun, tank, and submarine development. Claudius Dornier, the principal force behind the wartime Zeppelin-Staaken/Zeppelin-Lindau aircraft company, set up shop in Switzerland, just across Lake Constance from the wartime Zeppelin works. Junkers commenced building a celebrated line of water heaters in his German factories, while setting up aircraft production centers at Limhamn in Sweden and at Fili in the USSR. To fund development, he also set up airlines in Persia, Finland (Aero O.Y.), Sweden (A. B. Aerotransport), the Soviet Union (Deruluft), South America (SCADTA in Columbia and Aero Lloyd Bolivia), and elsewhere. Albatros set up its own industrial accommodation address in the free city of Memel, later Lithuania. Fokker continued to develop warplanes for Germany from his homeland, the Netherlands.
While there was thus no shortage of advanced airframes suitable for military use and no shortage of high-powered aeroengines (which could be obtained clandestinely from Western manufacturers desperate to unload wartime inventory), training and testing areas were hard to come by. Germany had a wealth of demobilized combat pilots in the 1920s. But few had managed to stay current on modern aircraft types, given the tight restrictions placed on aviation in Germany, Hungary, and Austria and the close attention that Allied, Polish, and Czech intelligence paid to enterprises in pro-German countries like Sweden and Finland. A less obvious location, closed to Western eyes, was clearly needed.
The German general staff found a solution in a most unlikely direction, the Soviet Union. From 1917, the German army had forced a series of humiliating and costly peace settlements on the Soviets while savagely repressing Bolshevik-inspired social and revolutionary movements at home and in the territories Germany occupied. From 1917 to 1918, German units supplied the Finnish generalissimo, von Mannerheim, with the force that destroyed the Red Finns. Indeed, the evidence suggests that the German command was ready to accept an armistice on almost any terms in order to free up troops for the Freikorps units that bloodily crushed the German Spartacist movement and the workers' Soviets in Bavaria and the Ruhr during the winter of 1918-1919. Yet, by 1924, Oberst Lieth-Thomsen was in Moscow with a team of German officers, negotiating a mutual assistance agreement with the Soviet air forces. In April 1925, the German and Soviet governments signed an agreement that gave Germany use of the Russian air base at Lipetsk, about 250 miles south of the Soviet capital, in exchange for technical advice and access to test results.
To equip the first flying unit of WIVUPAL, the Wissenschaftliche Versuchs- und Prüfanstalt für Luftfahrzeuge (Scientific Experimental and Test Establishment for Aircraft), as the Lipetsk operation was called, the Germans planned to use the all-metal Junkers Ju-22. The Ju-22 was a single-seat, fighter conversion of the Ju-21 two-seat reconnaissance machine then entering Soviet service. The main components of the two aircraft were essentially identical. Like the Ju-21, it offered such state-of-the-art features as jettisonable, externally mounted fuels tanks (on the fuselage sides), multitubular wing spars, and, of course, Junkers' trademark corrugated aluminum covering. But, to improve the pilot's view, the two-seater's parasol-type wing was lowered until it rested just above the fuselage decking. The former gunner's turret then became the pilot's cockpit. The Ju-22 was chosen because it had recently been selected as the standard fighter of the Red air forces. By using a Soviet type, the Germans hoped to further shield their new unit from attentions of Western intelligence services. Unfortunately, neither the Ju-21 nor the Ju-22 had flown at the time they were committed to production. When it was finally flight-tested, the Ju-22 proved disastrous. It was fairly fast for its day and could reach 150 mph. The radically altered wing position evidently reduced drag significantly. But it also changed the airflow over and around the aircraft's tail. This reduced the Ju-21's already marginal stability to an unacceptable degree. Worse still, the new forces generated by aerodynamic changes revealed a previously unsuspected lack of torsional rigidity in the rear fuselage structure. If the pilot tried to correct the type's inherent, high-speed instability with the rudder, the fuselage twisted, and the airplane snap-rolled and entered a spin. An use of the rudder in aerobatic flight generally resulted in complete loss of control. This and the poor view during take off and landing made the Ju-22 unacceptable as a fighter. It never entered production.
To replace the Ju-22s, the German staff decided to use 50 Fokker D-XIII fighters that had been purchased clandestinely during the Rhineland crisis of 1923. In that year, when Germany defaulted on some reparation payments, the French had occupied Germany's main industrial region, along the Rhine river. The German generals at one point planned to resist, and purchased fighters from their old supplier, now based in Holland. They took everything that Fokker had on hand—50 old Fokker D-XIs powered by the 300-hp Hispano-Suiza V-8 and 50 new D.XIIIs powered by the 450-hp Napier Lion W-12, the latter being the entire production run. Under cover of a fictitious Argentine order, the Germans managed to purchase the airplanes without interference from either the Dutch authorities or the Allies. But the anticipated need evaporated when it became clear that Germany was in no state for war, and the fighters went into storage in the Netherlands, for want of any other place to put them. After the failure of the Ju-22 program, German military authorities had the fully paid-for D.XIII fighters delivered to the Baltic port of Stettin for transshipment to Leningrad. The aircraft arrived in the USSR in May 1925, and fighter training began almost immediately.
The Fokker D.XIII was a slender sesquiplane of traditional and now rather old-fashioned Fokker construction—fabric-covered, welded steel-tube fuselage, and wooden wings. It was thus a far-cry from the technically advanced Ju-22. While the D.XIII set a number of records for speed with payload in 1925, it was only 10-mph faster than the Junkers aircraft, despite more than twice the horsepower. In service trim, it could reach 160 mph at 9843 ft and had a ceiling of 24,606 ft. It handled well, however, and seemed well-suited to the advanced-training role. It spanned 36 ft 1 in, was 25 ft 11 in long, and weighed 3637 lbs (maximum for takeoff). Range was 373 miles. In German service, the D.XIIIs were armed with a pair of synchronized, 7.92-mm MG.08 Maxim machine guns.
Once fighter training was under way, the Germans set about establishing an equivalent program for two-seat, general purpose airplanes. These were seen as the real workhorses of the air service. Their main jobs were reconnaissance, artillery observation, and infantry contact patrol work. But they also handled light bombing, ground-attack, and two-seat fighter missions, much as they had in WW1. Several aircraft types were considered for this role and tested at Lipetsk.
Originally, the German authorities favored the Junkers Ju-21 as their standard two-seater tactical trainer. This all-metal parasol monoplane was already in production at Junkers' Moscow-Fili plant and was expected to become the standard reconnaissance type of the Red air force. While its handling qualities were not as bad as those of the Ju-22 and while the reconnaissance role was inherently less demanding aerobatically, the Ju-21 nonetheless proved less than satisfactory. It was sluggish, awkward in maneuvering flight, and landed at an uncomfortably high speed. At 2800-lb fully loaded, the aircraft was fairly light by contemporary standards, and the designers had confidently predicted a maximum speed of 131 mph on the modest power of a 185-hp, war-surplus BMW IIIA six-cylinder engine. But the Ju-21 proved hard-pressed to reach a maximum of 122 mph, little better than the WW1-vintage De Havilland DH.9As it was meant to replace. The Junkers took 4.5 min to reach 3250 ft and had a ceiling of 18,428 ft. This was again comparable to the DH.9A, but, while the latter offered a 4-hour endurance, the Junkers could manage only 2.5 hours. The Ju-21 was, furthermore, unpopular in Soviet service and remained in use only until a Soviet copy of the more responsive DH.9A, the R-1, became available in 1926. German aviators were far less tolerant of poor flying qualities than their Soviet allies, so, given the likelihood that the type's Soviet service life would be short, the German general staff rejected the Junkers aircraft and looked elsewhere for a suitable two-seater.
After the failure of the Russian-built Ju-21, the Germans tried a series of clandestinely built German-made aircraft for the two-seater role. The airplanes were assembled by Heinkel and then smuggled out to Russia. The Albatros L.65 was evaluated at Lipezk, but rejected in favor of the competing Heinkel HD.17. Seven production Heinkels were purchased and delivered to Lipezk in 1926 (construction numbers 239-245). These were followed by six Albatros L-76a/L-77v reconnaissance machines with 600-hp BMW VI V-12 engines (c/n 10102-3, 10122-25). They spanned 41 ft 10 in and had a maximum speed of 137 mph at 4920 ft. The L-76/77 was replaced by the generally similar L-78 in 1928.
For the more specialized two-seat fighter/attack role (the CL-type aircraft, to use WW1 terminology), the Germans evaluated another, more successful Junkers type, the A.35 "postal aircraft" built at Fili and at Limhamn in Sweden. This was a low-wing monoplane of typical Junkers all-metal construction. It was similar in most respects to the wartime CL-1, but slightly larger all around. It spanned 52 ft 3.5 in, was 26-ft 11.75-in long, and weighed 3,527 lbs fully loaded. With its 350-hp Junkers L-5 six-cylinder engine, the A.35/K.53 could reach 128 mph and 20,000 ft. The Germans at Lipezk were able to convert the "civilian" A.35s to military K.53s simply by arming the aircraft with two synchronized, forward-firing MG.08s and a similar weapon in the rear cockpit, together with racks for light bombs under the fuselage and wings.
Small numbers of other types rounded out the German establishment at Lipetsk. A Rohrbach Roland, a Dornier B Merkur, a Junkers W.33, and a couple of Junkers F.13s filled the transport role. The Rohrbach and possibly some of the other transports were at one point armed and used to train medium-heavy bomber crews.
Curiously, most of the multiseat aircraft at Lipezk appear to have been armed with the LMG.08 Maxim as their standard turret weapon. This was a minimally modified version of the infantry's standard, heavy machine gun. By replacing the heavy sled-type mounting with a bipod and by fitting a wooden shoulder stock and pistol grip, the LMG.08 had made an overly heavy but acceptable squad machine gun. It was altogether too unwieldy to be a useful free-swinging aircraft gun, however. Presumably, the choice was made on the basis of availability rather than suitability for the purpose.
Training was not the only activity at Lipezk. Germany also tested many aircraft there, including the prototypes of the first generation of aircraft produced for the renascent German air service. In fact, in 1931, the German mission at Lipezk expanded from its normal training complement of 50-100 to over 200 to accommodate the ever more important test program. The new air force's first production fighter, the Arado Ar 64, was tested in prototype form in 1930, as the SD.II (c/n 52) and SD.III (c/n 54). Pre-production Ar-64s s/n 103 and 104 and Heinkel HD.45 and HD.46 reconnaissance aircraft followed in 1931. Dornier Do P, Do F, and Do 11 bombers and He 59 maritime aircraft (fitted with wheeled landing gear in place of floats) joined the test program in 1932.
By 1930, however, there was clearly no future in the Lipezk operation. The Soviets had long since realized that the arrangement was almost entirely one-sided. The Red air forces were gleaning little useful technical or tactical knowledge to offset the many advantages gained by these potentially dangerous, reactionary guests. Russian aviation was, in any case, on the verge of its golden age and had little need for the sort of limited assistance that the Germans might still provide. By 1930, Germany also had little to gain from the Lipezk operation. Once the initial cadres had been trained, Germany grew increasingly confident of its ability to train and, if necessary, to rapidly mobilize an air force on its own soil. Testing was becoming ever more awkward in German eyes, because of the potential for espionage. And finally, the deepening world depression made funds harder and harder to come by. In 1933, the Nazi party seized power, and the German school at Lipezk was finally closed after graduating some 230 pilots and observers. Two years later, the new regime was able to announce the existence of the newly renamed and reconstituted Luftwaffe to a fearful world.