Whether a Religious Order can be a Military Order?

Whether a Religious Order can be a Military Order?

From St. Thomas Aquinas, Summa Theologiae II-II.188.3:

I answer that, as stated before, a religious order may be established not only for the works of the contemplative life, but also for the works of the active life, insofar as it is concerned with helping our neighbor and the service of God, but not insofar as it is directed to a worldly object.

Now then, the military function can be directed to the assistance of our neighbor not only as regards private individuals, but also as regards the defense of the whole society. Hence it is said of Judas Machabeus (1 Mach 3:2,3) that he "fought with cheerfulness the battles of Israel, and he got his people great honor." The military function can also be directed to upkeep of divine worship. Wherefore (3:21) Judas is stated to have said: "We will fight for our souls and our laws," and further on (13:3) Simon said: "You know what great battles I and my brethren, and the house of my father, have fought for the laws and the sanctuary."

Hence, a religious order can be fittingly established for the military life, not indeed to fight for some worldly purpose, but for the defense of divine worship and public safety, or also for the poor and oppressed, according to the Psalm (81:4): "Rescue the poor, and deliver the needy out of the hand of the sinner."