In the late 1930s, the Heinkel concern of Germany began work on the world's first all-liquid fueled rocket-propelled aircraft. The idea of rocket propulsion was not a new one by this point in aviation history for several developmental airframes - mostly glider-type aircraft - took to the skies during the decade. All-liquid fueled rocket motors were a progressively better alternative to the solid-fuel offerings of the time concerning their use in aircraft. Heinkel began experimentation with such propulsion in 1936 and, by 1939, the technology had progressed to the point that the rocket-powered airplane was a very feasible subject. Foremost on the mind of Ernst Heinkel was the eclipsing of the then-standing world airspeed record which would bring national pride to Germany and notoriety to Heinkel itself. To achieve this feat, Heinkel envisioned an all-liquid fueled, rocket-powered aircraft utilizing a streamlined airframe and reaching speeds of 620 miles per hour.
Under the direction of Wilhelm Benz and Hans Regner, work began on a private venture design which became the "He 176". To begin with, the aircraft would be powered by a refined Walter HWK-R1rocket engine outputting 1,373lbs of thrust. The airframe would house the required fuel stores, avionics and single-seat cockpit. Key to its design would be the smallest possible airframe in an effort to delete all unnecessary aerodynamic-defeating protrusions and save on overall weight. The fuselage took on an aerodynamic approach with a glazed-over acrylic nose cone, cylindrical center section and tapered empennage. The tail unit included a conventional vertical tail fin and applicable horizontal tail planes. As speeds were projected to be rather intolerable for the feat at hand, the pilot would be given a reclined position to counter the effects of g-forces. The wings were short, small-area straight assemblies added to the middle of the fuselage sides, shoulder-mounted in place and slightly reminiscent of those as seen on the Heinkel He 111 Medium Bomber prior. The fuselage proved just large enough to house the intended components - measuring just 2.7 feet in diameter while the undercarriage was of the typical "tail-dragging" configuration of the time to include a pair of main landing gear legs and a tail skid along a narrow-track design. Due to this, skids were added to the wing tips to counter any possible tipping. The main landing gear legs themselves were fully retractable to help maintain aerodynamic qualities.
One of the more interesting design features of the He 176 was its pilot escape feature. As the intended airspeeds to be reached were truly monumental and very new territory, the He 176 was given a completely jettisonable cockpit section in the event of a catastrophic event during flight, leaving the rest of the fuselage to fall to its destruction with the pilot escaping (hopefully) without injury.
The first He 176 prototype was first flown on June 20th, 1939. However, the aircraft's performance was such that attending German Reich Air Ministry (RLM) officials were rather underwhelmed by the attempt. This particular rocket-fueled approach was not held in high regard both for its rather noisy execution and inherent dangerous nature concerning the combustible fuel. The He 176 even failed to surpass 435 miles per hour in her first flight attempt. As such, the He 176 project was not pursued beyond this developmental "peak" despite a second prototype on the drawing board. In the end, the airframe proved too heavy for the intended rocket powerplant - the thrust output rating not nearly consistent enough particularly during take-off actions and generally lackluster in straight-level flight. Additionally, the wing surface area was deemed too small for the required lift and control at the expected speeds, further dampening the performance numbers. From then on, the He 176 was sentenced as a museum piece, being sent to Berlin from Heinkel for public display in 1942. However, the Allied bombing campaign saw to it that the German capital was not out of its reach and responded accordingly, the He 176 being destroyed an air raid during 1943.
With the loss close of the He 176 rocket-propulsion project, Heinkel moved on to other endeavors. With Germany fully committed to war by this point - having moved politically and militarily across Europe to begin World War 2 - thought still centered on the use of high performance interceptor aircraft especially to counter the ever-growing threat of the allied bomber campaign wreaking havoc on German infrastructure and war-making capabilities. The RLM therefore moved on another similar aircraft initiative which ultimately produced the famous rocket-powered Messerschmitt Me 163 "Komet" - the first (and only) operational rocket-powered fighter anywhere in the world. This aircraft utilized an evolved form of the Walter rocket engine coupled with swept-back wings to which some 370 examples were ultimately produced, eventually seeing combat action against Allied aircraft in the air war over Europe. However, advances in jet technology made the age of the rocket-powered fighter short-lived.