Well... let's see;
Any soldier and member of armed forces (I have been in the navy of my native country) has the legal obligation to follow orders, some of which include the initiation of force (either in a preventive manner or in a deadly manner). This is by definition coersion. One cannot claim that under coersion they have choice of action, in order to be able to be deemed a moral agent.
A murderer, understands that he/she has the choice to NOT commit a murderous act, yet they do murder someone else. A murderer is not under coercion, he does have the ability to be a moral agent yet he avoids that possibility of choice
Therefore a soldier is not a murder. On the other hand he/she can become a murderer, if they use deadly action or preventive measures that result in death, while not under orders or inspite of instruction