It happened early Sunday morning at the Hilmar Grange Hall in Merced County.
Officials say four gang members began fighting with party goers, assaulting several of them.
Then, they tried to take off with cash donations for the departing soldier.
The Merced County Sheriff's Office arrested 19-year-old Lynn Thayer, 18-year-old Mario Ortega and 19-year-old Jesse Armenta for the attacks, along with a 17-year-old male.
They are all facing charges of armed robbery, assault, and being involved in a criminal street gang.