Proposed defense was a single turret manned by a dedicated gunner. This emplacement was armed with 2 x 30mm Mk 108 series autocannons to defend the aircraft from interception from trailing aircraft. The turret was situated directly aft of the cockpit to keep the crew together and improve communications between the members. Additional defense was through a similar turret mounted directly beneath the dorsal fitting - armed with the same weaponry and intended for defense of the aircraft's vulnerable underside. The undercarriage was jettisonable to simply construction and operation with landing by way of a skid system (similar in concept to the rocket-powered Messerschmitt Me 163 "Komet" interceptor).
In a February 1945 meeting, held at a time when the German war situation was decidedly desperate, the H.XVIII was selected ahead of competing long range, heavy bomber designs. The product was designated as the "H.XVIIIA" and engineers from both Messerschmitt and Junkers were involved to speed development. These engineers agreed that the Horten design could benefit from a more traditional, dedicated vertical tail fin fitted on the rear section of the fuselage to help improve directional controlling. The design decision was not well-accepted by the Brothers who took an evolved design, dimensionally similar though promising even greater operational ranges by way of 4 x Heinkel HeS 011 turbojets, to Hermann Goring himself. Goring was sufficiently impressed to order this newer design for construction as the "H.XVIIIB". The A-model proposal eventually fell to history with no real physical work having been completed before the end of the war.
The H.XVIIIB was a lighter overall design than the A-model before it and given a traditional wheeled undercarriage system that was not jettisonable. It also remained fixed in flight while faired over by an assembly that also was to house one of the HeS 011 turbojets each. Interestingly, the aircraft was to lack a nose landing gear leg and be supported through its multi-wheel main leg structures - a simplification for the manufacture process to an extent by doing away with a more complicated retracting undercarriage approach. Again, the multi-person crew (three) was to be held at the apex of the triangle design though now under a cleaner "bubble-style" canopy promising excellent views. Defensive armament was entirely optional as the operating altitude of the bomber would neutralize interception by Allied fighters. At any rate, the Hortens proposed 2 x 30mm MK 108 autocannons under the cockpit to satisfy any concerned authorities. Performance estimates included a maximum speed of 530 miles per hour and a range out to 6,835 miles while flying at altitudes of 52,500 feet. The end of the war in Europe in May of 1945 ended all work on the B-model - of which there was little tangible progress made as construction was not slated to begin until the fall of that year.
In one final revision - this one reportedly pushed by Messerschmitt and Junkers engineers - the H.XVIIIB H.XVIIIB-2 (also known as H.XVIIIC) was to feature 6 x BMW 003 turbojet engines under the wings and a dorsally-mounted turret armed with 2 x 20mm MK 151 cannons. Like all the other H.XVIII submissions, this too fell to naught.
While nothing became of the wartime H.XVIII program, Reimar Horten reestablished his work in Argentina following the end of the war. He managed to further his flying wing concept through the two-man DINFIA IA 38 prototype of which one was ultimately built and this first flown in December of 1960. The design proved to showcased poor performance because of its engines (4 x radial piston types of 450 horsepower each) and was ultimately abandoned, the hulk lost to a suspicious fire before being scrapped.
Work on flying wing concepts continued during the Cold War years, particularly in the United States by Northrop which its founder, Jack Northrop, had chased flying wing designs for decades - even in the prewar years as the flying concept was not solely a German venture. This eventually produced the Northrop YB-49, forerunner to today's highly-advanced B-2 "stealth bomber" (both detailed elsewhere on this site).
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