There were many German aviation concerns lending their talents to the war effort of World War 2 (1939-1945) but only a few stood above the others - Heinkel, Messerschmitt, Focke-Wulf being some of the more notable ones. While Heinkel's contribution is largely through its He 111 medium bomber series, it also tried its hand at a larger, more advanced multi-engined platform in the ultimately-failed He 177 "Greif" ("Griffon"). A unique compound engine arrangement was featured which coupled a pair of Daimler-Benz DB605 inline engines (as the DB610) but these proved prone to catching fire and several prototypes were lost in development. Structural issues only served to limit the type in production as fewer than 1,000 examples were seen by war's end - manufacture was actually ended earlier in 1944.
Back in April of 1942, the RLM initiated the "Amerika Bomber" program which called for a new long-range bomber featuring inherent endurance to bomb targets along the American East Coast following the United States' entry into World War 2 (December 1941). The range in question was about 3,600 miles and various companies threw their hat into the ring, various designs being contemplated which ranged from the conventional to the more advanced/bizarre. One final quality of the large aircraft would be provision to deliver an atomic bomb under development by German scientists before the end of the war.
The companies called to further their more conventionally-minded/conventionally-powered designs became Focke-Wulf, Heinkel, Junkers and Messerschmitt. For Focke-Wulf this became the Fw 300 and Ta 400 entries and Heinkel followed with their He 277 based on the aforementioned He 177. Junkers worked on their Ju 390 concept and Messerschmitt poured its resources into the Me 264. No one offering made it into operational service and eight prototypes (five from Junkers and three from Messerschmitt) was all there was to show for the late-war effort.
The He 177B was selected to form the basis of the He 277 submission. This represented a more conventionally-arranged, four-engine form of their compound-engined He 177A model. Thus, the complexities and engine troubles of the A-model were done away with and control issues were to be remedied by way of a twin-finned tail unit. Four engine nacelles were split as two per wing unit. A manned and a remote-controlled dorsal turret - along with a tail gun position, nose position and ventral chin/aft-facing position - would defend the aircraft from interception. A tubular fuselage was employed with a glazed-over nose section (as in the He 177A). The same "tail dragger" undercarriage seen in the He 177 would be reused in the He 277.
Power would come from 4 x BMW 801E 14-cylinder twin-row radial piston engines developing 1,975 horsepower each to which performance estimates included a maximum speed of 355 miles per hour, a maximum range of 3,728 miles and a service ceiling of 29,530 feet. The bomb load was 6,615 pounds total for trans-Atlantic sorties where fuel and weight-savings were important to range. Otherwise the type was cleared for up to 12,345 pounds of stores for more local missions with a 2,700 mile radius.
Despite the promising specifications, Heinkel could do little about German fortunes as the war deteriorated from 1944 into 1945. No prototypes were completed with only a few components fabricated by war's end (the He 277 project itself was cancelled back in April of 1944). With the shift to jet-powered bombers, it is doubtful the He 277 would have become a frontrunner for the Luftwaffe's long-range bomber need - which became increasingly focused on turbojet-powered types before the end and furthermore placed an emphasis on fighters and interceptors to counter the Allied bomber threat.
The He 277 ended as another German paper airplane and nothing more though the He 274 served as an offshoot of the program. This addition was also featured before war's end but amounted to two incomplete airframes which were taken over, and completed, by French industry. First flight of an He 274 was in December of 1945.