Related Rule
Philippines
Practice Relating to Rule 65. Perfidy
The Report on the Practice of the Philippines notes that officers of the Philippine armed forces make the distinction between ruses of war and acts of perfidy, adding that US military manuals are usually followed. 
Report on the Practice of the Philippines, 1997, Interview with a naval officer, 5 March 1997, Chapter 2.4.
At the CDDH, the Philippines, having in mind guerrilla warfare, supported the amendments proposed by Indonesia and Viet Nam to delete paragraph 1(c) of Article 35 of the draft Additional Protocol I (now Article 37) because “it would be basically unjust to brand the wearing of civilian clothing by a combatant as perfidy when such circumstances were brought about by the superior military strength of the aggressor”. 
Philippines, Statement at the CDDH, Official Records, Vol. XIV, CDDH/III/SR.28, 4 March 1975, p. 265, §§ 25 and 26.
However, the Philippines finally agreed upon paragraph 1(c) following the same reasoning as the one of Viet Nam stated below. 
CDDH, Official Records, Vol. XV, CDDH/III/SR.47, 31 May 1976, pp. 85 and 86, § 4.