Several aviation concerns of World War 2 fame (1939-1945) delved into the concept of Vertical Take-Off and Landing (VTOL) powered flight to which the Heinkel concern developed (and furthered) their study through the "Lerche" ("Lark") initiative (based on its earlier "Wespe" concept). The concept revolved around a streamlined, single-seat fuselage powered by two piston engines, the fuselage wrapped at its center by a large-diameter dual-prop fan system making use of a ducted-wing planform. Utilizing this arrangement, the aircraft - seated on its tail when on the ground at rest - could power up and lift itself from the earth vertically, reach a safe altitude and then lower its nose to begin its level flight phase. The pilot lay prone in the clear nose assembly. Such a design negated use of expensive and lengthy runway surface essentially allowing the Lerche aircraft to operate from just about any level surface - more importantly near the front before Allied bombers could reach valuable targets within German territories.
Design work began in February of 1945 though this proved much too late for the project to produce any physical fruit beyond drawings. German leader Adolf Hitler would commit suicide in late April and Germany would signal the end of the European war in May. Had the program been developed to a production-quality product, the Lerche system was to be classified as a fighter/interceptor and appropriately armed for the role through cannons and early guided missiles.
The definitive Lerche II was to be powered by 2 x Diamler-Benz DB 605D V12 liquid-cooled inline piston engines, each developing 2,000 horsepower (another listed alternative engine arrangement consisted of 2 x Daimler-Benz DB 503E series 12-cylinder inline piston engines, these producing an output of 2,400 horsepower). In either case, the Lerche would have utilized two contra-rotating propellers set at amidships within a ducted wing assembly to provide the desired lift/forward thrust. While performance specifications were wholly estimated (as no prototype was ever completed and no test aircraft flown), the Lerche was given a proposed maximum speed of 500 miles per hour with a cruising speed of roughly 340 miles per hour. Its service ceiling might have reached 47,000 feet while achieving a rate-of-climb equal to 9,800 feet per minute - a key quality for interceptors attempting to intercept incoming waves of enemy bombers in time.
As a fighter/interceptor aircraft, it was proposed for the Lerche design that it feature 2 x 30mm MK 108 cannons in side-mounted fuselage gun pods. There would also be support for 3 x Ruhrstahl X-4 air-to-air missiles - wire-guided missiles in development since June of 1943 under the direction of Dr. Max Kramer (though destined to never see combat action in the war). It essentially served as a predecessor to the guided missiles heavily featured in the upcoming Vietnam War (1955-1975).
Of course there proved too much innovation in the forward-thinking Lerche program and other issues would have led to an extended development period (shortage of resources, pilot training in VTOL flight, aerial combat through a non-conventional fighter airframe). It is presumed that special ladders would have had to be constructed for the pilot to reach the cockpit prior to entering. Many experts have, however, supported the aerodynamic qualities and concept of the Lerche design. Had it been given more design and development, it may have proven a useful vehicle.