Related Rule
Australia
Practice Relating to Rule 17. Choice of Means and Methods of Warfare
Australia’s Defence Force Manual (1994) states: “All feasible precautions [must be taken], in the choice of means and methods of attack, to minimise collateral damage.” 
Australia, Manual on Law of Armed Conflict, Australian Defence Force Publication, Operations Series, ADFP 37 – Interim Edition, 1994, § 556(e); see also Law of Armed Conflict, Commanders’ Guide, Australian Defence Force Publication, Operations Series, ADFP 37 Supplement 1 – Interim Edition, 7 March 1994, § 957(b).
With respect to precision guided weapons, the manual specifies:
The existence of precision guided weapons … in a military inventory does not mean that they must necessarily be used in preference to conventional weapons even though the latter may cause collateral damage. In many cases, conventional weapons may be used to bomb legitimate military targets without violating LOAC requirements. It is a command decision as to which weapon to use; this decision will be guided by the basic principles of LOAC: military necessity, unnecessary suffering and proportionality. 
Australia, Manual on Law of Armed Conflict, Australian Defence Force Publication, Operations Series, ADFP 37 – Interim Edition, 1994, § 834; see also Law of Armed Conflict, Commanders’ Guide, Australian Defence Force Publication, Operations Series, ADFP 37 Supplement 1 – Interim Edition, 7 March 1994, §§ 317 and 1024.
Australia’s LOAC Manual (2006) states that it is the duty of Australian Defence Force commanders to take “all feasible precautions, in the choice of means and methods of attack, to minimise collateral damage”. 
Australia, The Manual of the Law of Armed Conflict, Australian Defence Doctrine Publication 06.4, Australian Defence Headquarters, 11 May 2006, § 5.61.
In its chapter on “Air Operations”, the manual states: “The LOAC principles of proportionality, military necessity and unnecessary suffering determine which targets may be attacked by military aircraft”. 
Australia, The Manual of the Law of Armed Conflict, Australian Defence Doctrine Publication 06.4, Australian Defence Headquarters, 11 May 2006, § 8.36.
The LOAC Manual (2006) replaces both the Defence Force Manual (1994) and the Commanders’ Guide (1994).