Related Rule
Practice Relating to Rule 14. Proportionality in Attack
Section A. General
Nigeria’s Military Manual (1994) states:
Every commander has … to respect the rule of proportionality, i.e. the use of proportional military force so as to avoid causing incidental civilian casualties and damage which is excessive in relation to the value of the expected result of the whole operation. 
Nigeria, International Humanitarian Law (IHL), Directorate of Legal Services, Nigerian Army, 1994, p. 42, § 11.
Nigeria’s Manual on the Laws of War states: “In any case of attack or bombardment of a defended locality, the killing and destruction must be proportionate to the military advantage sought.” 
Nigeria, The Laws of War, by Lt. Col. L. Ode PSC, Nigerian Army, Lagos, undated, § 13.
According to the Report on the Practice of Nigeria, it is Nigeria’s opinio juris that the rule of proportionality forms part of customary international law. 
Report on the Practice of Nigeria, 1997, Chapter 1.5.
The report also notes that the principle of proportionality was violated by the Nigerian air force on numerous occasions during the civil war. Senior military officials and aircraft pilots were reported to have regretted such violations. 
Report on the Practice of Nigeria, 1997, Chapter 1.5, referring to The War in the Air, New Nigerian War Souvenir Edition, 12 January 1970.