At that time powered aircraft construction was banned in Germany by the Versailles Treaty, so he established a second factory in Copenhagen.

[1] The Ro III had a cantilever high wing of strictly rectangular plan and thick aerofoil section.

[1] The Ro III was powered by a pair of 270 kW (360 hp) water-cooled V-12 Rolls-Royce Eagle IX engines strut-mounted close together above the wing, their propellers well ahead of the leading edge.

Stability on the water was provided by long, stepless floats on each side, strut-mounted from the wings a little outside the engines and braced to the fuselage with a parallel pair of horizontal struts.

Like some other Rohrbach flying boats, the Ro III carried a pair of masts and sails, to be used if the aircraft was forced to put down at sea without engine power.

[1] The new variant was more powerful, with two 340 kW (450 hp) Lorraine 12E Courlis W12 water-cooled engines in shorter and more streamlined cowlings, with their honeycomb radiators on the wing underside below them.

After four years of operation, they were given a lengthy examination by the German aviation authorities, who found them in good order and with no safety problems.