:drillsergeant:
Pacifism is not Catholic, period!  Pacifism is for cowards, fαɢɢօts, and sincere but mistaken heretics.  A good point was made about an enlisted man participating in an unjust war, however, who determines if a war or combat situation is just?  Is that the job of an enlisted man?  If so, there will be as many judgments as soldiers.  An individual soldier must determine whether his specific actions in battle are just.  Example, he may not obey an unjust command, ie. execute children in a daycare center belonging to the enemy to make him afraid. (That is murder.)  However, if the children are killed as the unintended result of a legitimate battle in the street outside, or the bombing of a known military target, no sin is committed.  Is it a terrible tragedy for which the enemy may legitimately seek recompense?  Yes, it is.  One must keep in mind that war is a punishment for sin, but God Himself is a Warrior.  
If the combat soldier goes into battle in a state of grace, obeys a just command, and commits no mortal sin (three conditions met) during the fighting, then he can be at peace that even if he is killed, he is in a state of grace.  There are no doubt countless Catholics who have saved their souls in combat, who, had they lived to return, may have fallen away and gone to Hell.
 :dancing-banana:

(This is not addressed to Frances exclusively or specifically)

As far as the enlisted man's responsibility to determine whether the cause is just or not, I think it's indisputable that he must, as a volunteer, do this.

Now, at the same time, it's perfectly conceivable and realistic that he could be fooled (in good will) to believe a war is just when it isn't-- and naturally, other factors like his motivations are taken into account, the point being that there are many contributing factors to the morality of the volunteer soldier going to war.

However, objectively speaking, I don't see how one can join the modern American military.  In doing so, one is swearing to kill, if necessary, to defend a country founded by freemasons with (at best) deistic principles and (at worst) downright Satanic motives.  These are not things that a Catholic could knowingly defend without incurring some form of guilt on his soul.

I think that there are good men in the military, valiant men in the military, and even that valiant acts are performed in modern military service.  But ultimately, these good things are incidental to someone ignorantly doing something that they shouldn't be doing (or in many other cases, wantonly doing what they shouldn't be doing).  We shouldn't pretend that "a few good men" who perform outstanding and valorous service lend legitimacy to an industry which exists to enforce a corrupt government and it's evil principles.  Those acts of valor and sacrifice are anomalies in the face of an ugly war machine, using propaganda to lure naively patriotic pawns into it's endgame.  

This isn't about pacifism.  Everyone knows that pacifism, as such, is not a Catholic principle.  After all, David writes "Blessed be God who maketh my hands to fight and my fingers to war."  This isn't about being pacifistic, this is about avoiding the pitfalls of Americanism, democracy, and misguided patriotism-- all of which contribute to duping good young men into joining the military, with the empty and vain promise of glory.