Jim was a soldier and first member of Franklin Lawler's Armoured Soldier Program. He underwent an 18 month program of both steroid and surgical enhancements to prepare his body to wear the original Arsenal exosuit armour. He wore that armour in the field until it was eventually decommissioned and he retired and replaced by B.A.S.S.
Shortly after Jim's retirement, the Heroes Unite Commander, Natasha Lawler crossed the line and Franklin Lawler took command of Heroes Unite to bring her and Nemesis into custody. Franklin brought in his Armoured Soldier program to assist (although B.A.S.S appears to have been operating with the Heroes Unite Initiative already). Franklin asked Jim to return from retirement as Arsenal and Jim was happy to oblige.
The Arsenal Suit was destroyed by Nemesis.
Following his stint in New Guard (Team), Jim Tanner takes the decision to retire the Arsenal suit and returns to his role as an active Colonel in the military.
Arsenal wears a suit of powered exoskeletal armour capable of heavy firepower including lasers and missiles. His current "Crescendo" suit also has boot jets which allow him to fly.
Jim's original Arsenal ("Armoured Soldier Mach I") suit was older and less powerful than the B.A.S.S. ("Armoured Soldier Mach II") one. However, he is now wearing the upgraded "Crescendo" suit and his new suit is cutting edge.