After hearing that both Maj. Emelifonwu and Maj. Ogunro were murdered by Hausa-Fulani soldiers in Kaduna, Lt. Col. Kalu made his way to a railroad depot where he managed to stow away inside the water-tank of a train destined for south-eastern Nigeria.

Kalu was given command of the 52nd Brigade by President Ojukwu after the Nigerian 3rd Marine Division under Gen. Benjamin Adekunle seized Bonny with little resistance in July 1967.

Again, in late March and early April, after a series of reversals, Kalu blocked the first major attempt by Adekunle to take Port Harcourt through Onne.

Kalu quickly fell out of favor with the local Biafran civilian leaders in Port Harcourt due to his inability to clear the area of the Nigerian threat and, consequently, was relieved of his command of the 52nd Brigade by President Ojukwu and replaced by Maj. Joseph Achuzie on May 19, 1968.

After 5 days of fierce urban warfare, Port Harcourt fell to the Nigerian 3rd Division under Gen. Adekunle while the Biafran 52nd Brigade was forced to retreat to Igrita.

After staging these guerrilla attacks that caused the Nigerians to suffer mass casualties, the 63rd Brigade soldiers slipped back into Biafran held territory with only minimal damage.

After Owerri was captured by two battalions of Nigerian soldiers, Kalu was made commander of the Biafran 14th Division and given strict orders in a letter written to him by President Ojukwu.

On April 24 the 300 Nigerian soldiers still under Col. Etuk's command began staging a breakout of Owerri and managed to escape to Nigerian-held territory after a day of heavy fighting against the Biafran troops surrounding the city.