The first of these new versions, V4, was completed in June 1936. It featured the new, elliptical wing, a more powerful 210Da engine with a two-speed supercharger that brought the power to 514 kW (690 hp) for takeoff and a smaller tailplane, while it also sported two fuselage-mounted 7.92 mm MG 17 machine guns. V3 was modified to a similar standard.

A prototype, known as Heinkel He 112 V5, was designed and built by engineer Wernher von Braun, who would later design the V-2 rocket. This variant of the fighter He 112 was powered by an additional rocket engine. First flown in early 1937, the He 112 V5 demonstrated the feasibility of rocket power for aircraft.

In July, both V5 and V6 were completed. V5 was identical to V4, with the Jumo 210Da engine. V6, on the other hand, was completed as the pattern aircraft for the A series production run, and thus included the 210C engine instead of the more powerful, but less available Da. The only other change was a modification to the radiator, but this would not appear on later A-0 series models. V6 suffered a forced landing on 1 August and was repaired and joined V4 for testing in October.

The last of the prototype A-0 series was V8, which was completed in October. It switched engines entirely and mounted the Daimler-Benz DB 600Aa, along with a three-bladed, fully adjustable, all-metal propeller. The engine was a huge change for the aircraft, producing 716 kW (960 hp) for takeoff and had 33.9 L (2,069 in³) displacement at 686 kg (1,510 lb), compared that to the Jumo 210Da's 514 kW (690 hp) from 19.7 L (1,202 in³) at about the same weight. V8 was seen primarily as a testbed for the new engine, and more importantly, its cooling systems. The DB used a dry liner in the engine that resulted in poor heat flow, so more of the heat was removed by oil as opposed to water, requiring changes to the cooling systems.

In March 1937, the aircraft was assigned to rocket propulsion tests at Peenemünde. It completed these tests later that summer (without exploding) and was returned to the factory, where it was converted back into a normal model. At the end of the year, it was sent to Spain, where it was seriously damaged on 18 July 1938. Once again, it was put back together and was flying four months later. Its fate after this time is not recorded.

Production models
At this point, the prototype stage was ostensibly over, and Heinkel continued building the A-0 as production line models. The naming changed, adding a production number to the end of the name, so the next six examples were known as He 112 A-01 through A-06. All of these included the 210C engine and were essentially identical to V6, with the exception of the radiator.

These aircraft were used in just as varied a manner as the earlier V series had been. A-01 flew in October 1936 and was used as the prototype for a future 112 C-0 carrier-based aircraft. It was later destroyed during rocket tests. A-02 flew in November, and then joined the earlier V models at Rechlin-Lärz Airfield for further testing in the contest. A-03 and A-04 were both completed in December, A-03 was a show aircraft and was flown by Heinkel pilots at various air shows and exhibitions, A-04 was kept at Heinkel for various tests.

The last two models of the A-0 series, A-05 and A-06, were completed in March 1937. They were both shipped to Japan as the initial machines of the 30 for the Imperial Japanese Navy.

He 112B
Prototypes
In October 1936, the RLM changed the orders for the zero series 112s, instructing Heinkel to complete any A-0s already under construction and then switch the remaining aircraft to an updated design. This gave Heinkel a chance to improve the He 112, which they did by completely redesigning it into an almost entirely new aircraft called the He 112B. It is at this point that it became a modern design that could compete head-to-head with the Bf 109.

The He 112B had a completely redesigned and cut-down rear fuselage, a new vertical stabilizer and rudder, and a completely enclosed cockpit with a bubble-style canopy. The canopy was somewhat more complex than later bubble designs; instead of having two pieces with the majority sliding to the rear, the He 112B's canopy was in three pieces and the middle slid back and over a fixed rear section. Even with the additional framing, the He 112 still had excellent visibility for its day. Armament was also standardized on the B model with two 7.92 mm MG 17 machine guns in the sides of the cowling with 500 rpg, and two 20 mm MG FF cannons in the wings with 60 rpg. For aiming, the cockpit included the then-modern Revi 3B reflector gunsight.

The first B series airframe to be completed was V7 in October 1936. V7 used the DB 600Aa engine like the A-series V8, and it also used the original V1 style larger wing. This wing was later replaced with a smaller one, but instead of the clipped version from the earlier V models, a completely new single-spar fully elliptical wing was produced. This design became standard for the entire B series. V7 was turned over to von Braun in April 1937 for yet more rocket tests, and managed to survive the experience. It was then returned in the summer and sent to Rechlin where it was used as a test aircraft.

The next type was V9 which flew in July 1937, powered by the 507 kW (680 hp) Jumo 210Ea engine. V9 can be considered to be the "real" B series prototype, as V7 had received the DB 600Aa originally for experimental reasons. The entire surface was now flush riveted and the aircraft had several other aerodynamic cleanups. The radiator was again changed, this time to a semi-retractable design for reduced drag in flight. The aircraft also underwent a weight reduction program which reduced the empty weight to 1,617 kg (3,565 lb).

As a result of all of these changes, the V9 had a maximum speed of 485 km/h (301 mph) at 4,000 m (13,120 ft), and 430 km/h (270 mph) at sea level. This was a full 20 km/h (10 mph) faster than the contemporary Bf 109B. Nevertheless, by this time, the Bf 109 was already ramping up production, and the RLM saw no need for another largely similar aircraft. It is also worth noting that users of the aircraft generally found it impossible to reach this speed, and rarely managed to exceed 418 km/h (260 mph).

Heinkel He 112V-10
[Source: Unknown]

The last prototype, V12, was actually an airframe taken off the B-1 series production line (which had started by this point). The Jumo 210Ea was replaced with the new fuel-injected 210Ga, which improved performance of the engine to 522 kW (700 hp) for takeoff, and a sustained output of 503 kW (675 hp) at the reasonably high altitude of 4,700 m (15,420 ft). Better yet, the Ga also decreased fuel consumption, thus increasing the aircraft's endurance. The new engine gave V12 such a boost that it became the pattern aircraft for the planned B-2 series production.

With all of these different versions and experimental engine fits, it might seem like every aircraft differed significantly. But with the exception of the engine fits, the Bs are all basically identical. Due to the shortage of just about any German engine at the time and the possibility that advanced versions could be blocked for export, various models had to be designed with different installations. Thus the B models were different only in their engine, the Jumo 210C in the He 112 B-0, the Jumo 210Ea in the B-1, and the Jumo 210Ga for the B-2.

Production models
In order to show off the He 112, V9 spent much of the later half of 1937 being flown by pilots from all over the world. It was also sent around Europe for tours and air shows. The effort was a success and orders quickly started coming in. However, a variety of problems meant few of these were ever delivered.

The first order was from the Imperial Japanese Navy, who had a requirement for a fast climbing interceptor to deal with Tupolev SB bombers over China. After seeing V9 in flight, they quickly placed an order for 24 112Bs, with an option for 48 more. The first four were shipped in December 1937, another eight in the spring, and promises for the rest to arrive in May. Before delivery, the Luftwaffe unexpectedly took over 12 of the aircraft to bolster its forces during the Sudetenland Crisis. The aircraft were then returned to Heinkel in November, but the Japanese, who were unhappy with the high maintenance workload and lower manoeuvrability compared with fighters like the Mitsubishi A5M, refused to accept them this late and Heinkel was left holding the aircraft.

In November 1937, an Austrian delegation came to see the aircraft, led by Generaloberst Alexander Löhr, Command-in-Chief of the Luftstreitkräfte (Austrian Air Force). Test pilot Hans Schalk flew both the Bf 109 and the He 112V9 back to back. Although he felt that both models performed the same, the Heinkel had more balanced steering pressures and better equipment possibilities. They placed an order on 20 December for 42 He 112Bs. Pending the license for the MG FF cannon, these aircraft would remove the cannon and add six THM 10/I bomb shackles which carried small 10 kg (22 lb) anti-personnel bombs. The order was later reduced to 36 examples due to a lack of funds (the He 112B cost 163,278 Reichsmarks), but the aircraft were never delivered due to the annexation of Austria in the March 1938 Anschluss.

Spain was so impressed with the He 112's performance during evaluation in the civil war that the Spanish Air Force purchased the 12 aircraft in early 1938, and later increased the order by another six (some sources say five). Of the first 12, two were shipped in November, another six in January, and the rest in April.

In April, it looked like Yugoslavia would be the next user of the He 112. It placed an order for 30 aircraft, but later cancelled the order and decided to produce other designs under license.

Finland appeared to be another potential customer. From January–March 1938, the famous Finnish pilot Gustaf Erik Magnusson travelled to Germany to gain experience in new tactics. He had been on similar tours in France in the past and was interested to see how the Germans were training their pilots. On a visit to the Heinkel plant in Marienehe, he flew the He 112 and reported it to be the best aircraft he had flown. In May, Heinkel sent the first of the He 112 B-1s to Finland to join an air show. It remained for the next week and was flown by a number of pilots, including Magnusson, who had since returned to Finland. Although all of the pilots liked the aircraft, the cost was so high that the Suomen Ilmavoimat (Finnish Air Force) decided to stick with the much less expensive Fokker D.XXI.

A similar setback would accompany sales efforts targeting the Dutch Air Force, who was looking to purchase 36 fighters to form two new squadrons. A He 112 B-1 arrived for testing on 12 July and quickly proved to be the best aircraft in the competition. Nevertheless, they decided to purchase the locally built (and rather outdated) Koolhoven F.K.58 instead. The aircraft was not ready for production, so in an odd twist, they then purchased a number of Hawker Hurricanes because they could be delivered immediately. In the end, the F.K.58s were never delivered.

Fortunes would be seem to be reversed with Hungary. In June 1938, three pilots of the Magyar Királyi Honvéd Légierö (Royal Hungarian Home Defense Air Force or MKHL) were sent to Heinkel to study V9. They were impressed with what they saw, and on 7 September, an order was placed for 36 aircraft, as well as an offer to license the design for local construction. Through a variety of political mishaps, only three aircraft were ever delivered and licensed production never happened.

The final and perhaps most successful customer for the He 112B was Romania. The Forţã Aeronauticã Regalã Românã (Royal Romanian Air Force) ordered 24 aircraft in April 1939, and increased the order to 30 on 18 August. Deliveries started in June, with the last being delivered on 30 September.

By this point, war had broken out, and with better models on the market - including Heinkel's own He 100 - no one else was interested in purchasing the design. The production line was closed after a total of only 98 aircraft, 85 of those being the B series models.

He 112R
Early experiments with rocket propulsion
In 1931, the Army Weapons Office testing ground at Kummersdorf had taken over research into liquid-fuel rockets. In 1932, Wernher von Braun designed a rocket of this kind which used high percentage spirit and liquid oxygen. With this he made the first experiments. In 1934 he fired his second rocket type, the A2, from the North Sea island of Borkum. Having completed the programme of experiments, von Braun was interested in evaluating an aircraft with a rocket motor propulsion system. For this he needed an aircraft and support team. Initially the highest levels at the Army High Command and the Reich Air Ministry (RLM) were opposed to such "fantasies", as they called them. Many people, technicians and academic experts in positions of influence in aeronautics, maintained that an aircraft driven by a tail thrust would experience a change in the centre of gravity and flip over. Very few believed the contrary, but one of them was Ernst Heinkel. Following his offer of unhesitating support, Heinkel placed at the disposal of von Braun an He 112 fuselage shell less wings for the standing tests.

In 1936 von Braun had advanced far enough to begin trials. A great tongue of flame from the rocket motor roared through the fuselage tail to set up the back thrust. Late in 1936 Erich Warsitz was seconded by the RLM to Wernher von Braun and Ernst Heinkel, because he had been recognized as one of the most experienced test pilots of the time, and because he also was technically proficient. Warsitz wrote:

"For the later flight trials Heinkel gave us an airworthy He 112 which we fitted with an additional rocket motor, and after months of untiring effort we started to look for somewhere to carry out the flight experiments under conditions of secrecy and reasonable safety."

The RLM agreed to lend Neuhardenberg, a large field about 70 kilometres east of Berlin, listed as a reserve airfield in the event of war. Since Neuhardenberg had no buildings or facilities, a number of marquees were erected to house the aircraft. In the spring of 1937 the Kummersdorf Club transferred to Neuhardenberg and continued the standing trials with the He 112 fuselage.

In June 1937 Erich Warsitz undertook the initial flight testing of the He 112 fitted with von Braun’s rocket engine. Despite the wheels-up landing and having the fuselage on fire, it proved to official circles that an aircraft could be flown satisfactorily with a back-thrust system through the rear.

Also the firm of Hellmuth Walter at Kiel had been commissioned by the RLM to build a rocket engine for the He 112, so there were two different new rocket motor designs at Neuhardenberg; whereas the von Braun’s engines were powered by alcohol and liquid oxygen, Walter engines had hydrogen peroxide and calcium permanganate as a catalyst. Von Braun’s engine used direct combustion and created fire, the Walter produced hot vapours from a chemical reaction, but both created thrust and provided high speed. The subsequent flights with the He 112 used the Walter-rocket instead of von Braun's; it was more reliable, simpler to operate and the dangers to test pilot Erich Warsitz and machine were less.

After conclusion of the He 112 tests using both rocket motors, the marquees at Neuhardenberg were dismantled at the end of 1937. This coincided with the construction of Peenemünde.