Cyborg 009 is a story about nine experimental cyborgs (eight male and one female), which have been collected by the evil terrorist group, Black Ghost. Those nine cyborgs with the aid of a scientist turn against Black Ghost's control. Black Ghost in turn starts sending more cyborgs to destroy their first nine experimental cyborgs and causing destruction all around the world.

(Source: AnimeNfo)

Episodes 1-48 aired on TV. Episodes 49-51 consist of the "GOD'S WAR" OVA. An additional recap episode aired between episodes 47 and 49.
The "GOD'S WAR: Prologue" bonus arc is not intended to be in continuity with the other episodes, as it was instead produced as a teaser at adapting the unwritten final chapter of the Cyborg 009 manga. TV Tokyo could not air more than 51 episodes and the first two OVA episodes were cut and merged together into one episode, leaving the final one unaired.

(Source: Cyborg009 Wiki)