During the mid 1930s, Generalleutnant Walther Wever, a longtime advocate of strategic bombing, pressed the Luftwaffe to develop a dedicated long-range bomber for the role of attacking the Soviet Union's factories in the Ural Mountain area.

This concept was received with significant skepticism amongst many senior officials within the Luftwaffe and, by 1936, this "Ural bomber" program had delivered two rather uninspiring designs, the Dornier Do 19 and Junkers Ju 89.

Usually, a 7.92 mm MG 81 machine gun in a flexible mount was positioned in the upper starboard side of the cockpit nose glazing for defense against frontal attacks.

"[11] Tests on the 40th production A-1 aircraft in September 1942, revealed serious outer wing panel component damage after only some 20 flights, due to the aerodynamic stress from diving attack exercises.

That same day, the Oberkommando der Luftwaffe (OKL/Luftwaffe High Command) stipulated that the new design should possess sufficient structural strength to enable it to undertake medium-degree diving attacks.

The engine nacelles and wings had little room for the main undercarriage members, which needed to be longer than usual, for ground clearance for the large diameter four-blade counter-rotating propellers.

Francke was pleased with the general handling and landing characteristics of the prototype but complained of some vibration in the airscrew shafts, the inadequacy of the tail surfaces under certain conditions, and some flutter which accompanied any vigorous movement of the elevators.

Photographs of the first eight prototypes show a largely circular fuselage cross-section, especially forward of the wing root, with the A-0 series possessing flatter sides, dorsal and ventral surfaces of the main A-series production aircraft.

Starting in August 1943, all He 177's delivered had an extended rear fuselage - by 1.60 m (5 ft 3 in) - to both instill greater stability for bombing accuracy[24] (see Airworthiness and handling section) and to offset the slightly lengthened engine nacelles (a "stretch" by 20 cm (7.9 in)) and the associated centre of gravity change.

To reduce the aircraft's weight, no firewall had been provided, and the aft end of each DB 606 was fitted so close to the main spar — with the rear two-thirds of the component powerplants' engine blocks being placed behind the wing's leading edge — that there was insufficient space for the fuel/oil fluid lines and electrical harnesses.

Insufficient lubrication caused disintegration of the connecting rod bearings, which sometimes resulted in conrods bursting through either one of the component engine crankcases and puncturing oil tanks.

The first of the experimental weapons fitments known to have been tested was the 12 examples of the He 177A-1/U2 Zerstörer variant, which was armed with a pair of limited-traverse 30 mm MK 101 cannons in the extreme front of a dramatically enlarged Bola ventral gondola (beyond the hemispherical "fishbowl" nose glazing), and intended for ground attack, train busting, and possibly long-range anti-ship raids.

[40] One development proposed during 1943 was to create a chin turret using the earlier Hecklafette's quadmount gun elevation assemblies to either side of a new, remote-control traverse core as the Bugstandlafette BL 131V, located at the forward end of the He 177A's Bola undernose gondola.

However, engineering studies of the quadmount chin turret project revealed that its fitment, proposed for a number of the later He 177A variants and the He 177 V104 prototype airframe, would lower airspeed by about 30 km/h (19 mph) and reduce the deployable bombload by a full tonne, making the BL 131V concept unacceptable, and prompting the idea of using a chin-turret mount version of the FDL 151Z twin-cannon remote turret instead for the B-series, four-DB 603 engined He 177Bs, close to what had been pioneered with the GI+BP airframe early in 1943.

[42] Flight testing of the He 177 in late summer 1942 revealed deficient stability around the yaw and pitch axes, resulting in extremely poor bombing accuracy when using the Lotfe 7 bombsight.

[43] Shortly after these tests, the third production A-1 example (factory serial number 15153, with Stammkennzeichen of GI + BN) had its fuselage lengthened by 160 cm (63 in) just aft of the trailing edge of the wing.

The modified aircraft, with the longer distance of the "tail moment", showed a marked degree of improvement in yaw and pitch axis stability, enough to mandate the construction of the He 177A-3 and all subsequent models of the He 177A with the lengthened fuselage.

A transport and two escort fighters from the RAE flew to the area to leave the Royal Aircraft Establishment Chief Test Pilot Roland Falk and a flight engineer with the commando group.

Ernst Udet was also critical before the war of the coupled DB 606 powerplant choice for the He 177, with Göring voicing his own frustrations with the seemingly interminable engine problems delaying the introduction of the He 177A into service.

Göring was reported as stating in late August 1942, following his earlier complaints to Oberst Petersen on the 13th of the month: "I had told Udet from the start that I wanted this beast with four engines.

Although no photographs are known to exist verifying their fitment, the general arrangement Typenblatt drawing for the V101 airframe — bearing the "B-5" subtype designation within the drawing's title block[51][failed verification] — showed that it was intended to be uniquely fitted with a small-area matching vertical pair of so-called pivoting "drag rudders" mounted, one per side, a short distance in from the horizontal stabilizers' tips, directly inline with the inner engine nacelles, to simulate "engine-out" conditions.

Because flight testing had revealed that the single-tailed V101 exhibited an increasingly serious stability problem with higher airspeeds, the subsequent prototype, the V102, was both the first He 177B example to fly, on 20 December 1943, with the quartet of DB 603 engines, in combination with a brand-new empennage of twin tail configuration, fitted to it during the early autumn of 1943.

[52] On 24 February 1944, as the USAAF's Big Week strategic bombing campaign against Germany continued, particularly against targets in northern France involving V-weapons installations — a meeting was held at the all turf-surfaced Wiener Neustadt military airfield.

Erhard Milch, and fellow guests Oberst Edgar Petersen and Oberstleutnant Siegfried Knemeyer (Göring's top aviation technology expert), each had a chance to fly the now four-engined V102 prototype after the B-series set of wings had been fitted.

[55][56][failed verification] One additional surviving photo, showing what looks like a He 177B-series prototype from the right side with a production-style A-series single vertical tail surface set, and bearing the Stammkennzeichen code of NE+OD,[57] does not match any item of the surviving documentation for the four known 177B-series prototypes ordered, built or flown before the end of the war,[58] and possessing one of the upgraded, upright-seating A-5 subtype's tail gunner's emplacements, as well as the usual twin dorsal turret defensive armament of the He 177A-5 subtype.

It had sustained damage from a bad landing in April 1944 while evading one of the initial USAAF 15th Air Force raids on the area, which had kept it from being flown north to the Luftwaffe's Rechlin test facility for safety.

In an assessment of the aircraft on 9 April 1942, the newly activated Erprobungsstaffel 177 reported that the Greif had good flying characteristics, but had unacceptable engine troubles and problems with its airframe strength.

As an emergency measure, aircraft from Kampfgeschwader 50[65] were used to supply the encircled 6th Armee at Stalingrad, where they were found to be unsuited for the transport role, carrying little more cargo than the smaller and more reliable Heinkel He 111, and proving useless for the evacuation of wounded.

These aircraft were brand new, delivered a week before the operation and not fully flown in, because the air unit had moved to a new airfield the day before and lacked sufficient maintenance personnel and material.

[69] On the Eastern Front, the most notable action by the He 177 was a mass raid of some 87 aircraft against railway targets in the Velikiye Luki area, about 450 km (280 mi) west of Moscow on 19 July 1944.