JAG is the acronym for Judge Advocate General.

Jesus will return to Judge the Word and as a General in war, he will come and make war in the end times (Revelation 19:11). He is not only a Judge and General but an Advocate as well, for if we sin, he intercedes for us with God the Father (1 John 2:1).

Jesus is the ultimate Judge Advocate General (J.A.G)

Revelation 19:10-11 (KJV)
10 And I fell at his feet to worship him. And he said unto me, See thou do it not: I am thy fellowservant, and of thy brethren that have the testimony of Jesus: worship God: for the testimony of Jesus is the spirit of prophecy.
11 And I saw heaven opened, and behold a white horse; and he that sat upon him was called Faithful and True, and in righteousness he doth judge and make war.

1 John 2:1-2 (KJV)
1 My little children, these things write I unto you, that ye sin not. And if any man sin, we have an advocate with the Father, Jesus Christ the righteous:
2 And he is the propitiation for our sins: and not for ours only, but also for the sins of the whole world.