Related Rule
Netherlands
Practice Relating to Rule 101. The Principle of Legality
The Military Manual (1993) of the Netherlands provides with respect to non-international armed conflict: “Nobody may be condemned for acts or omissions which did not constitute a punishable act at the time of the act or omission in question.” 
Netherlands, Toepassing Humanitair Oorlogsrecht, Voorschift No. 27-412/1, Koninklijke Landmacht, Ministerie van Defensie, 1993, p. XI-5.
The Military Manual (2005) of the Netherlands states: “A prisoner of war may not be sentenced for an act which was not punishable at the time when it was committed.” 
Netherlands, Humanitair Oorlogsrecht: Handleiding, Voorschift No. 27-412, Koninklijke Landmacht, Militair Juridische Dienst, 2005, § 0747.
In its chapter on non-international armed conflict, the manual states that “[n]o derogation is possible from the [prohibition] of … penalties heavier than applicable at the time of the offence”. 
Netherlands, Humanitair Oorlogsrecht: Handleiding, Voorschift No. 27-412, Koninklijke Landmacht, Militair Juridische Dienst, 2005, § 1020.
In its chapter on non-international armed conflict, the manual states:
Section 11 - Prosecutions and procedural guarantees
1071. The prosecution and punishment of offences relating to the armed conflict should be subject to the following conditions (this relates to the bearing of arms and the committing of offences and war crimes during the internal armed conflict):
- no one may be convicted of an offence that was not punishable by law at the time it was committed. 
Netherlands, Humanitair Oorlogsrecht: Handleiding, Voorschift No. 27-412, Koninklijke Landmacht, Militair Juridische Dienst, 2005, § 1071.
In its chapter on peace operations, the manual states:
Section 2 - Applicability of human rights
1211. Human rights should be respected … However, “in time of war or in case of any other general state of emergency which threatens the existence of the country,” certain human rights may be curtailed as long as the situation strictly necessitates such measures. But the right to life, the prohibition of torture, slavery and forced labour, and the legal principle “no punishment without prior legal provision” cannot be waived. 
Netherlands, Humanitair Oorlogsrecht: Handleiding, Voorschift No. 27-412, Koninklijke Landmacht, Militair Juridische Dienst, 2005, § 1211.