2265: Legitimate defense can be not only a right but a grave duty for one who is responsible for the lives of others. The defense of the common good requires that an unjust aggressor be rendered unable to cause harm. For this reason, those who legitimately hold authority also have the right to use arms to repel aggressors against the civil community entrusted to their responsibility.
While not a full blown treatment of Just War doctrine/theory, it certainly seems to me to absolutely rule out the hard-core pacifist position.