The Nigerian Civil war, which broke out in 1967 was fought by the Federal Government of Nigerian against the defunct Eastern Nigeria region that had declared itself the sovereign state of Biafra. The Federal Government of Nigeria sought to keep the region as a Nigerian entity while the defunct region sought to secede. This study focuses on the Battle of Onitsha; one of the most significant battles in the Civil war, owing to the strategic location of Onitsha. A brief background to the battle is also given for a better understanding of the trend of the Onitsha operation by both forces as the city was important to the contending parties. The paper reveals that the outcome of this Battle boosted the moral of the Federal forces although the Biafran troops continued to fight until the end of the war in 1970. The study further analyses the resilience, improvisation, and defensive ingenuity of Biafran forces, whose effective use of terrain, observation posts, mines, and the locally produced Ogbunigwe significantly shaped the course of the campaign. The aftermath, including the Abagana ambush, reveals the vulnerability of overstretched logistics and the limits of tactical victories achieved without sustained operational support. Drawing from these events, the work identifies critical lessons for future commanders relating to strategic adherence, force preparation, discipline, intelligence, terrain appreciation, logistics security, adaptability, and the role of innovation in warfare.