High Quality Content by WIKIPEDIA articles! The R.VI was the most numerous of the R-bombers built by Germany, and also one of the first closed-cockpit military aircraft (but the first was Russian aircraft Sikorsky Ilya Muromets). The bomber was reputedly the largest wooden aircraft ever built until the advent of the Hughes H-4 Hercules built by Howard Hughes, its wingspan of 138 feet 5.5 inches (42.2 m) nearly equaling that of the World War II B-29 Superfortress.