I am very well aware that there are those who are called reformed/calvinists who are pro military for christians.
Others who are not known to be reformed/calvinists, but rather known by many other names, who'd fall into the arminian/protestant camps are pro military for christians as well.
Since some have, or would, brand all who'd be called reformed/calvinists as pro military for christians I offer these words from one who would certainly fall under the reformed/calvinist camp. Here are his words:
"Salvation (not swords nor spears, but the salvation of our God) will God appoint for walls and bulwarks." Not only are they not required or needed, but they are most positively forbidden. All our trust and reliance for protection and safety must be in God. He is himself a wall of fire round about his people, and the glory in their midst. In this particular is the church of God manifestly distinguished from all anti-Christian churches or religious organizations. In all ages, worldly religion has relied on worldly support and worldly protections. At this very day there is a mighty howling among the shepherds of anti-Christ, and those religious denominations who have been the principal promoters of the dreadful scenes of carnage which has just swept over our country, desolating what was the fairest portion of the earth, slaughtering hundreds of thousands of our fellow-men, and both at the North and the South are now appealing to the worst passions of men to aid in procuring from the secular powers a law for the suppression of those religious orders which they deem antagonistic to their interests, pleading that their religious establishments are in danger by reason of the Roman Catholics, and all others who will not pander to them. They staining the earth with a crimson tide ask, and even demand that the sword of state shall be drawn for the suppression of those whom they proscribe as heterodox, and for their own defense. They take the sword, rely upon the sword, and with sword shall they perish. But it is not so with the church of the living God.
Not only has the cause of God and his church always been sustained without aid or protection of human governments, but in opposition to all the powers of earth and hell, and always in such a manner as to clearly show that God is himself the strength of Israel, and the Savior thereof in the time of trouble. His name is their strong tower, and in his pavilion where he has hidden them they have perfect safety. We perfectly agree with brother Purington that Christians are forbidden to use carnal weapons for the defense of the kingdom of God, which being "not of this world," cannot be sustained by the power of this world. But the question arises, and perhaps was intended by "E. H.,"Are Christians allowed, by the laws of Christ, to use the sword, or carnal weapons, in any case, or under any circumstances whatever?" The more we have reflected upon this subject, the deeper our convictions have become that the precepts, as well as the spirit of Christ in his saints, forbid it. Every essential requisite for a Christian disqualifies him for carnal warfare. To be a disciple of the meek and lowly Lamb of God, we must have his spirit and temper; and except we have it we cannot be his disciple. While to fit men for carnal warfare they must be bold, daring, defiant, aspiring, and unpitying. To be a disciple of Christ we must love our enemies, do good to them who despitefully use and persecute us; but to be a soldier in carnal warfare, we are forbidden to sympathize with our enemies, or to give them aid or comfort, on pain of penalties provided in the laws of human warfare
The Christian then, to be a soldier in carnal warfare, must abandon the laws of Christ and submit to the military code; must disobey the commands of Christ, and obey the opposite commands of military chieftains. How truly are we told, "No man can serve two masters." How can we possibly obey both when one commands us to kill, and the other forbids us to kill? When one commands us to love, pray for, and do good to our enemies, and the other commands us to fight, rob, harass and destroy them? The example of Christ is given as an infallible guide to all this children, and in that example he went about doing good to all classes of men, friends and foes; healing the sick, feeding the hungry, and showing compassion to all who were in distress; in all his walks he was holy, harmless, undefiled, and separate from sinners, and he commands his disciples to follow him. And he says, "Except a man deny himself, and take up his cross, and follow me, he cannot be my disciple."
The recruiting officers of Caesar would reject such men as really and truly follow Christ as unfit for a pace in their army. What do they want of men who love their enemies, or who will not kill, or rob, or spoil their enemies? But while the meek, lowly, loving, sympathizing Christian would be rejected, they would greatly prefer carnal professors and graceless hypocrites, who go in the way of Cain, whose feet are swift to shed blood, and before whose eyes there is no fear of God, and of whom it is said, Misery and destruction are in all their ways. Such are the men for carnal warfare; those who are led by the spirit, temper and example of him who was a murderer from the beginning, and abode not in the truth. But those who strictly follow him who came not to destroy mens' lives, but so save them, would only be in the way in earthly warfare.
But it is urged that Christians are to "be subject to the powers that be, and to obey those who are in authority over them." This is very true, but at the same time they are told that there is no power, or authority but that which is of God. Usurpation is not legitimate power, and usurpers have in reality no authority to enjoin on the subjects of Christ's government anything that Christ has forbidden; for Christ is himself the only blessed potentate, the King of kings, and Lord of lords. In everything wherein God has invested kings, governors, rulers or judges of the earth with power or authority over the citizens of the world, the Christian is, by the laws and commandments of Christ, required to honor and obey them, to that extent, but no further. Whether it be right for Christians to obey men rather than God, judge ye. If Caesar commands us to kill, and God commands us, saying, "Thou shalt not kill," which is to be obeyed? Or if rulers of the earth forbid the minsters of Christ, as in the case of Peter and John in Acts 5:29, to preach in the name of Christ, and God has commanded them to preach, is it hard to determine which is the higher power, or which is to be obeyed?
It is said that some Christians have been compelled to take up arms, and to slaughter their fellow men. This may be so; but we do not know of a case in which a Christian, how as conscientiously opposed to carnal warfare, viewing it a violation of the law of Christ, who has made his appeal in solemn prayer to God for deliverance, and has not been delivered. But even if it were so, if the Christians were actuated by the same mind which was evinced by the martyrs of former times, would they not sooner suffer death themselves than yield to violate the law of Christ by killing their fellow men?
Let the church of God take her position as a city set upon a hill, whose light cannot be hidden; and let it be known that come life, or come death, her members cannot be forced to shed the blood, or destroy the property of their fellow men under any circumstances whatever, then we doubt whether the governments of the world would have use for such soldiers as they would make. But should they persist, we might look for a divine interposition, or if brought to the test, God would give us grace to bear all the consequences. it is not strange, as the case now stands, that the governments of the earth should regard the conscientious scruples of Christians as unimportant and trifling. For while nearly all the anti-Christian orders of religionists not only sanction, but absolutely occupy a leading position in all the wars that agitate the world, the church has been slow, very slow indeed, to declare her position and say to the world that she will, under no circumstance, stain her hands with blood. But instead of holding this position, has not the church been faulty in withholding her light upon this subject; and have not, some at least of the members voluntarily entered the field of carnage, or advocated the shedding of blood; and when the matter has been submitted to the voice or vote of the people, have not some, even of the members of the church of God, the professed disciples and followers of the Prince of Peace, given their voice, their vote, and the full measure of their influence for war, to the bitter end? How is this to be reconciled with the command of God to "Follow peace with all men, and holiness, without which no man shall see the Lord?" There are many examples given of Christ and his apostles, and the primitive saints, resisting evil even unto the death, striving against sin, but in all cases refusing the use of carnal weapons. But in what part of the sacred volume have we an account of Paul, applying to Nero for a Major or Brigadier General's commission, or Peter asking for and army contract, or even of the loving John preaching war sermons, and making war speeches to induce the disciples of the Lamb to enter the army? Even if we had such examples left on record, we are forbidden to follow them; for we are only to follow even the apostles as far as they followed Christ. And Christ, when he was reviled, reviled not again; and he has commanded his disciples to "Avenge not themselves; to resist not evil with evil." If smitten on one cheek, to turn the other cheek also to the smiter, and to remember the word of instruction, "Vengeance is mine; I will repay, saith the Lord." If God thus claims the sole right of arbitration and retribution, and if he has as positively forbidden us to avenge ourselves, is it not irreverent and presumptuous for us to usurp the ministration of wrath and vengeance in his stead? Let those who know no God and therefore fear him not indulge their cruel passions; but, Christians forbear! Let not the sun go down on your wrath. Appeal not to the sword, lest by the sword ye perish!
I could furnish what others who'd be called reformed/calvinist have written against being pro military for christians, but the above will suffice to show that there are those in that camp who are far from being pro military for christians.