I searched via Google for causes of Court Martial, for treason on duty/in office, for serious offences, abuse of materiel, favouritism. Unfortunately the situation I am thinking of is way too specialized to come up even in a reasonably like way.
So now I am seeking input from people who have indepth knowledge of military matters and offenses officers can commit.
Note: the military body in question is fictive, but either going by US forces regulations or by a joined international army in a war situation (like during WWII) would be ideal.
A commander of a large military unit (think army-sized) of major importance to the combined efforts of many countries (like UNO) in an ongoing war and his second in command both have access to a variety of army material (airplanes, attack vehicles, submarines, jets etc.). A family member of the commander has been hurt and needs a special kind of medicine only available on another continent. Time is of the essence, else that family member will die.
A transporter airplane filled with tanks happens to be waiting for take-off on this continent and the commander orders it to leave there 12 hours earlier than it was scheduled - with the medicine aboard. So far no concrete harm is done, except that the staff has a slightly shorter furlough. No one would notice the slight deviation from schedule and the plane will anyway arrive where it is needed, namely in London (thus not detour), and it would bring the needed medicine in time.
During that flight a situation in that ongoing war occurs which necessitates that the transporter delivers the tanks inside it to a different destination (Ireland). The second in command gives the order for the transporter to detour to Ireland and deliver the vehicles. With them there is a chance to rescue an extremely important spy of the enemy and this might win that war. The second in command has no knowledge about the medicine on board the transporter and he has no knowledge of the family member of the commander being on the brink of death. The commander is by the way his best friend, that sick family member is quite beloved by that second as well.
The commander learns about the detour which will most certainly result in the medicine arriving too late. The delay means the death of his family member. He is aware that his second would again detour the transporter to London if he knew about the whole problem, regardless of the offence he would commit by doing so. So he says nothing. The family member does die as a result.
I need to know what would be the most likely offence of the second in command, in case he would detour the transporter again (by this condemning to death the spy who might turn the war).
Would that be straight treason? Or dereliction of duty? Or ... what?
What would be the result, if court martialled? Would the second be condemned to death?
Just to give a hint, another officer in that army was once condemned to death for leaking confidential, yet non-essential data to the public.