Related Rule
Switzerland
Practice Relating to Rule 37. Open Towns and Non-Defended Localities
Section C. Attacks on open towns and non-defended localities
Switzerland’s Basic Military Manual (1987) states: “It is prohibited to attack or bombard, by whatever means, undefended cities, villages, housing areas or buildings.” 
Switzerland, Lois et coutumes de la guerre (Extrait et commentaire), Règlement 51.7/II f, Armée Suisse, 1987, Article 32(1).
The manual further provides that “launching an attack against non-defended localities” constitutes a grave breach of the 1977 Additional Protocol I. 
Switzerland, Lois et coutumes de la guerre (Extrait et commentaire), Règlement 51.7/II f, Armée Suisse, 1987, Article 193(1)(d).
Switzerland’s Military Criminal Code (1927), taking into account amendments entered into force up to 2011, states in a chapter entitled “War crimes”:
Art. 110
Articles 112–114 apply in the context of international armed conflicts, including in situations of occupation, and, if the nature of the offence does not exclude it, in the context of non-international armed conflicts.
Art. 112
1 The penalty shall be a custodial sentence of not less than three years for any person who in the context of an armed conflict directs an attack against:
c. … undefended settlements or buildings … that are not military objectives. 
Switzerland, Military Criminal Code, 1927, taking into account amendments entered into force up to 2011, Articles 110 and 112(1)(c).
Switzerland’s Penal Code (1937), taking into account amendments entered into force up to 2011, states under the title “War crimes”:
Art. 264b
Articles 264d–264j apply in the context of international armed conflicts, including in situations of occupation, and, if the nature of the offence does not exclude it, in the context of non-international armed conflicts.
Art. 264d
1 The penalty shall be a custodial sentence of not less than three years for any person who in the context of an armed conflict directs an attack against:
c. … undefended settlements or buildings … that are not military objectives. 
Switzerland, Penal Code, 1937, taking into account amendments entered into force up to 2011, Articles 264b and 264d (1)(c).