At the danger of boring everyone about the argument of the legality or otherwise of the 2003 Iraq War and the subsequent occupation, the legal position is as follows.
1. International law is largely based on obligations freely accepted by states - in other words, in signing up to a treaty, a country agrees to play by the rules that that treaty imposes. For our purposes, the most important treaty is the UN Charter, which at Article 2(4) makes the use of force between states illegal, with two exceptions;
(i) force authorised by the UN Security Council under a Chapter VII resolution or
(ii) self-defence, when there is no option but to defend yourself (this is the so-called "Caroline" test after a case between the UK (in Canada) and the USA in the early 19th Century) .
A third exception has been postulated for actions to stop humanitarian disasters, which is controversial amongst international lawyers and which I personally support.
(this was the basis of the 1999 Kosovo Campaign).
2. As a result, international law trumps individual country's laws, so if it's illegal in international law, it cannot be legal in domestic law. (Brick: this is the same principle as US Federal Law trumping US State laws).
3. The 2003 attack itself (Op IRAQI FREEDOM / Op TELIC) was illegal - it was not authorised by the Security Council and it was not self defence. It was also not covered by the humanitarian exception.
As a result, as the attack was illegal, orders for the 2003 attack were also illegal.
HOWEVER:
The UN Security Council authorized the occupation force in UNSCR 1483 of 22 May 2003 which has subsequently been renewed, provides the Chapter VII resolution required for the use of force. So no orders subsequently issued to deploy are illegal per se, and should be followed.
It is this that Flt Lt Kendall-Smith and this American Lt fall foul of, because they are failing to obey legal orders, and will (correctly and comprehensively) have the book thrown at them, irrespective of the moral courage that they have shown.
S41