Related Rule
South Africa
Practice Relating to Rule 155. Defence of Superior Orders
South Africa’s LOAC Manual (1996), referring to the South African Constitution (1996), provides: “A person who commits a war crime pursuant to an order is guilty of a war crime if that person knew or should have known that the order was unlawful.” 
South Africa, Presentation on the South African Approach to International Humanitarian Law, Appendix A, Chapter 4: International Humanitarian Law (The Law of Armed Conflict), National Defence Force, 1996, § 44.
South Africa’s Medical Services Military Manual provides: “When an order is manifestly illegal the subordinate has the duty to refuse to obey. The order will not be a ground of justification in such a case, it will not justify his/her acts.” 
South Africa, Medical Services Military Manual – Humanitarian Law, South African Medical Service Academy in Voortrekkerhoogte, s.d, p. 5.
South Africa’s Revised Civic Education Manual (2004) states:
59. … A person who commits a war crime pursuant to an order is guilty of a war crime if that person knew or should have known that the order was unlawful. …
60. When problems arise in this regard, it is usually because orders are unclear. Commanders at all levels should strive to give clear, easily understood orders. This is vital in combat. Soldiers should be encouraged to ask for clarification if in doubt as to the legality of an order. Commanders should not put soldiers in a difficult position of trying to decide whether an order is lawful or not. 
South Africa, Revised Civic Education Manual, South African National Defence Force, 2004, Chapter 4, §§ 59–60.
South Africa’s ICC Act (2002) provides with regard to genocide, crimes against humanity and war crimes:
Despite any other law to the contrary, including customary and conventional international law, the fact that a person –
(b) being a member of a security service or armed force, was under a legal obligation to obey a manifestly unlawful order of a government or superior,
is neither –
(i) a defence to a crime; nor
(ii) a ground for any possible reduction of sentence once a person has been convicted of a crime. 
South Africa, ICC Act, 2002, § 4(2).
In the Werner case in 1947, a South African Court of Appeal rejected a plea of superior orders in a case in which the accused, himself a prisoner of war, was convicted for the murder of another prisoner. It held: “[The German officer] had no authority to give orders, and the appellants were under no duty to obey them, even if those orders had not been so obviously illegal that they should have known them to be illegal.” 
South Africa, Appeal Division, Werner case, Judgment, 20 May 1947.