Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 15. The Principle of Precautions in Attack
Section C. Feasibility of precautions in attack
The UK LOAC Manual (2004) states:
With respect to attacks, the following precautions shall be taken:
(1) those who plan or decide upon an attack shall:
(b) take all feasible precautions in the choice of means and methods of attack with a view to avoiding, and in any event to minimizing, incidental loss of civilian life, injury to civilians and damage to civilian objects. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 5.32; see also § 13.32 (maritime warfare).
The manual further states: “‘Feasible’ means that which is practicable or practically possible, taking into account all circumstances ruling at the time, including humanitarian and military considerations.” 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 5.32, footnote 191.
Upon signature of the 1977 Additional Protocol I, the United Kingdom stated: “The word ‘feasible’ means that which is practicable or practically possible, taking into account all circumstances at the time including those relevant to the success of military operations.” 
United Kingdom, Declarations made upon signature of the 1977 Additional Protocol I, 12 December 1977, § b.
Upon ratification of the 1977 Additional Protocol I, the United Kingdom stated that it understood the term “feasible” as used in the Protocol to mean “that which is practicable or practically possible, taking into account all circumstances ruling at the time, including humanitarian and military considerations”. 
United Kingdom, Reservations and declarations made upon ratification of the 1977 Additional Protocol I, 28 January 1998, § b.
The United Kingdom further stated that the obligation mentioned in Article 57(2)(b) of the 1977 Additional Protocol I only applied to “those who have the authority and practical possibility to cancel or suspend the attack”. 
United Kingdom, Reservations and declarations made upon ratification of the 1977 Additional Protocol I, 28 January 1998, § o.