Operation OAU, (September 2 – October 15, 1968), was a battle between Nigerian 3 Marine Commando Division (3MCDO) and Biafran 12 Division in modern day south-eastern Nigeria. Operation OAU was an intermittent battle which may have resulted in over 25,000 deaths on both sides. Although the Biafran soldiers were outnumbered they were able to retain control of Umuahia and eventually recapture the cities of Owerri and Aba.