all fifty were delivered to front-line units in may, where they proved popular but after only 10 hours of service the engines started showing serious problems, overheating and seizing. siemens blamed the problem on the voltol-based oil that was used to replace scarce castor oil for lubricating the engine but the type was withdrawn from service and replaced by fokker d.viis. when they were removed, rudolf berthold, commander of jg.ii, noted that he felt "the siemens fighter be made available again for front-line use as quickly as possible for, after elimination of the present faults, it is likely to be become one of our most useful fighter aircraft".