The R7 was originally built in 1934 as a prototype, and production plans were scrapped as World War II spread across Europe. The R7, which was more heavy and expensive to build than BMW would have liked, was stripped of some useful parts and put away in a box.
In 2005, the R7 was brought back into daylight, and BMW Classic rebuilt the bike, which has suffered corrosion over the years. Now the bike, which many consider a masterpiece ahead of its time, is operational again. http://www.nextautos.com/over-70-years-later-bmw-r7-prototype