Siemens - Schuckert R . II The Siemens - Schuckert R . II was a prototype bomber aircraft built in Germany during World War I . It was one of six aircraft based on the Siemens - Schuckert R . I that were originally intended to be identical , but which each developed in a different direction and were designated as different aircraft types by the German Inspectorate of Flying Troops ( the Idflieg ) . Although the R . II was the first of the batch to be completed , it was the last accepted into military service , and then only as a trainer . Design and development . As designed , the R . II was a large three - bay biplane with unstaggered wings of unequal span and a fully enclosed cabin . Power was to be supplied by three 180 - kW ( 240 - hp ) Maybach HS engines mounted internally in the fuselage , which transmitted their power via driveshafts to two propellers mounted tractor - fashion on the interplane struts nearest the fuselage . The main undercarriage consisted of divided units , each of which carried dual wheels , and the tail was supported by a pair of tailwheels . The fueslage was forked into an upper and lower section , which allowed a clear field of fire to the rear of the aircraft . The R . II first flew on 26 October 1915 and was delivered to the military on 20 November . The Maybach engines proved immediately troublesome , prone to overheating and mechanical failure . In February 1916 , the engines were removed and returned to the manufacturer . Ongoing trouble with the same engine in other aircraft eventually led Siemens - Schuckert to abandon work with these engines entirely and in June , the firm asked the " Idflieg " whether to install Benz Bz . IV or Mercedes D . IVa in the R . II instead . By the time that the " Idflieg " approved the Mercedes engine for installation , Siemens - Schuckert did not have the workforce available to install them , and placed the R . II in storage instead . While the R . II was in storage , the " Idflieg " changed its requirements for the aircraft , requesting that the operational altitude be increased from 3 , 000 m to 3 , 500 m ( 9 , 800 ft to 11 , 000 ft ) , but hoping that even more altitude would be possible . Siemens - Schuckert responded that this would not be possible with the Mercedes engines recently approved for installation , and suggested three Benz D . IV engines inside the fuselage , augmented by two more of the same engine mounted pusher - fashion in the interplane gap . The " Idflieg " rejected this suggestion , insisting on the basic requirement of having the engines serviceable in flight . By the time that workers were available for the R . II again , in early 1917 , Siemens - Schuckert had gained experience with the similar R . VII and attempted to meet the " Idflieg " ' s requirements by installing extra sections in the wing to extend it to six bays and thereby offset the extra weight of the new engines . The upper wings were replaced with a new design with greater chord , and the tail surfaces were enlarged . Finally , bomb racks were fitted to the wings that could carry either six 50 - kg bombs or four 100 - kg bombs . During its acceptance flight , the newly refurbished R . II carried a 2 , 310 - kg ( 5 , 100 - lb ) useful load to an altitude of 3 , 800 m ( 12 , 000 ft ) and stayed aloft for four hours . Having satisfied requirements , R . II was delivered to " Riesenflugzeugersatzabteilung " ( Rea — " giant aircraft support unit " ) , the support unit for R - type aircraft , on 29 June 1917 . Although the R . II ' s performance was a significant improvement over other R - type aircraft produced by Siemens - Schuckert , its increased span and weight limited its speed , and it could not keep pace with similar aircraft manufactured by Staaken then entering service . The R . II was therefore relegated to training duties with the " Riesenflugzeug Schulabteilung " ( " giant aircraft training unit " ) at Döberitz . In June 1918 , it was transferred back to Rea at Cologne , where it crashed later that year .