The Siemens-Schuckert R.I was a bomber aircraft built in Germany during World War I.^[4][5] It was originally ordered as the Siemens-Schuckert G.I prior to the German Inspectorate of Flying Troops (the Idflieg) adopting the "R" classification for multi-engine aircraft in late 1915.^[6] Some sources refer to the aircraft as the Siemens-Schuckert Steffen R.I, including the name of the brothers that designed it.^[1]

The R.I was a large three-bay biplane with unstaggered wings of unequal span^[7] and a fully enclosed cabin. Power was supplied by three 112-kW (150-hp) Benz Bz.III 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.^[8] The main undercarriage consisted of divided units, each of which carried dual wheels, and the tail was supported by a pair of tailwheels.^[2] The rear fuselage structure was forked into an upper and lower section, which allowed a clear field of fire to the rear of the aircraft.^[1] The entire structure was of wire-braced wood, covered in fabric.^[2]

Designers Bruno and Franz Steffen piloted the aircraft themselves on its first test flight on 24 May 1915.^[2] They ended this flight prematurely because of overheating in the gearboxes,^[2] and subsequent tests revealed other defects such as excessive vibration in the drive system.^[9] With these problems addressed, the R.I was ready for its Idflieg acceptance flights in June 1915.^[9] Bruno Steffen ferried the three-person inspection team, plus a number of passengers, from Neumünster to Döberitz.^[9] He had even placed two armchairs and a bottle of champagne in the cabin for the occasion.^[9] The R.I reached Döberitz safely and made around twenty-four test flights before it was accepted by the military on 26 July 1915.^[6]

On 13 October 1915, the R.I was assigned to Feldfliegerabteil 31, a reconnaissance unit, at Slonim.^[6] However, a series of mishaps and malfunctions prevented it from seeing any operational use and the R.I was dismantled and sent back to Berlin by rail in March 1916.^[6] Although damaged in transit, the R.I was repaired and was assigned to the Riesenflugzeugersatzabteilung (Rea — "giant aircraft support unit") as a trainer from mid 1916 to 1918 — possibly even to the Armistice.^[10]

Parts of the R.I were preserved in a Berlin museum until destroyed by bombing during World War II.^[3] Despite the difficulties encountered with the design, the Idflieg was sufficiently impressed with the R.I to order a batch of six similar aircraft on 26 June 1915, to be powered with the more powerful Maybach HS engine in place of the Benz B.III used by the R.I.^[11] Although the six were originally intended to be identical, each developed in a different direction and were eventually designated as different aircraft types by the Idflieg — R.II, R.III, R.IV, R.V, R.VI, R.VII.^[12]

The R.I was ordered and delivered as the Siemens-Schuckert G.I in the G (Grossflugzeug - large aircraft) series and given serial number SSW G.I 31/15, changed to SSW G.I 32/15 before the final change to R.I/15.^[6] Similarly, the Siemens-Schuckert R.II to R.VII were ordered in the G (Grossflugzeug - large aircraft) series and given serial numbers G.32/15 to G.37/15 respectively. These serials were changed on 13 July 1915 to G.33/15 - G.38/15, for unknown reasons and again on 6 November 1915 to R.2/15 - R.7/15 in the R (Riesenflugzeug - giant aircraft) series, adopting the R.II to R.VII designations.^[12]