I'll try to keep this as short as possible historically. Germany obviously needed a 4-engine strategic bomber to hit Britain and then ultimately the US eastern seaboard. Heinkel responded immediately with a proposed uncoupled version of the He-177A as He-277. Goering and the RLM refused while Messerschmitt was allowed to proceed with its Amerika Bomber- the Me-264. Heinkel didn't take "No" for an answer and proceeded with conversion of a He-177A-5 creating the misleading designation He-177B-5 which led to the RLM finally allocating the designation He-277 by 1943! This had 4x DB 603 engines, but suffered poor performance and stability issues having tried a single tail, split tail, and even a triple tail configuration! Meanwhile, in France at SAUF, Heinkel used local manufacture of components to modify a He-177A-4 into what would become the He-274 strategic bomber. All supervision and assembly was undertaken by Heinkel. Production went amazingly slow as this was started in 1941 and nearing completion by July 1944 when the Germans were retreating from France. The aircraft could not fly and was left abandoned along with a second aircraft and a third airframe just started. Although the French caused delays, it is a myth to believe that this alone caused the aircraft to be lost. The He-274 also had problems with pressurization, hydraulics, stability, and design of the remote weapon systems to all be controlled from the cockpit with 4-5 man crew. The planned ejection seats did not work either. What's really bad about all this is that this was started back when the He-177 originated and had it gone forward in Germany with Goering's approval, this machine would have been used against Britain and was much more powerful and capable. The 274 was powered by 4x DB 603 engines @ 1850 hp each. It had a top speed of 363 mph at height, a ceiling of nearly 47,000 ft, and range (depending on mofel and loads carried) of between 2600-3600 miles! Its weapon systems would have been anywhere from 8-12 remote MGs in nose, dorsal, ventral, and tail installations plus add-on ASMs or rockets for anti-shipping. Internally it could carry 3-4 tons of bombs, aerial mines, and potentially a tactical German A-bomb or radiological weapon. Back to history... it fell to the French that completed the V1 and V2 and first flew in December 1945 at Orleans-Bricy. The two bombers were used as test aircraft from 1948-53 and then scrapped. Launched a glider version and influenced the SO.4000 jet bomber prototype. The two Me-264s were also delayed and bombed in 1944 with a total loss of both. Horten began construction of the next jet Amerika Bomber as Ho-XVIII in March 1945 with little completed by May 1945. The USSR contemplated building the Horten flying wings for use against the US but declined as too complex for mass production!

http://www.airwar.ru/image/i/bww2/he274-i.jpg
http://www.luftarchiv.de/flugzeuge/heinkel/he274_1.jpg
SO.4000:
http://www.aviastar.org/pictures/france/so_4000.jpg
*Sud-Ouest