Complex sentence: The autobahns were not primarily intended as major infrastructure improvement of special value to the military as often stated, because they were of no military value as all major military transports in Germany were done by train to save fuel.
Split into simpler sentences: The autobahns were not primarily intended as major infrastructure improvement of special value to the military as often stated. Their military value was limited as all major military transports in Germany were done by train to save fuel.