Israel-Gaza: What the law says about the fighting

The legal manual used by the British armed forces says that military necessity allows a state to use force, unless otherwise prohibited, which is “required in order to achieve the legitimate purpose of the conflict, namely the complete or partial submission of the enemy at the earliest possible moment and with the minimum expenditure of life and resources”. The argument that the Israeli bombardments on Gaza are ineffective because they have always failed to stop rocket attacks may, in one sense, evidence the futility of the use of force in this context. But, from a military necessity angle, it may justify the use of greater force as is necessary to achieve the objective of averting the attacks.

source: bbc.com