https://en.wikipedia.org/wiki/Deus_vult
Robert the Monk, who re-wrote the Gesta Francorum c. 1120, added an account of the speech of Pope Urban II at the Council of Clermont in 1095, of which he was an eyewitness. The speech climaxes in Urban's call for orthodoxy, reform, and submission to the Church. Robert records that the pope asked Western Christians, poor and rich, to come to the aid of the Greeks in the East:
When Pope Urban had said these and very many similar things in his urbane discourse, he so influenced to one purpose the desires of all who were present, that they cried out, 'It is the will of God! It is the will of God!' When the venerable Roman pontiff heard that, with eyes uplifted to heaven he gave thanks to God and, with his hand commanding silence, said: Most beloved brethren, today is manifest in you what the Lord says in the Gospel, "Where two or three are gathered together in my name there am I in the midst of them." Unless the Lord God had been present in your spirits, all of you would not have uttered the same cry. For, although the cry issued from numerous mouths, yet the origin of the cry was one. Therefore I say to you that God, who implanted this in your breasts, has drawn it forth from you. Let this then be your war-cry in combats, because this word is given to you by God. When an armed attack is made upon the enemy, let this one cry be raised by all the soldiers of God: It is the will of God! It is the will of God![18]
I'm not saying that I approve of Hegseth's deus vult tattoo, but I would point out that it's quoting one of your predecessors.