In A.G. 164 he was the base commander of the Earth Federation's Luna Base, however he defected to the Vagan, along with Girard Spriggan. It is revealed that he planned Reina's "accident" which caused her to lose her loved one, which was the start of her hatred for the Federation. This was all to recruit her to his cause when he defected to the Vagans, as she served as a bargaining chip for him.
During the Federation assault on the Luna Base, he is put in charge of the defenses of Luna Base by Zeheart Galette when Zeheart sorties in the xvt-zgc Ghirarga. Eventually one Federation team, the Abis team, is able to break into the base. Simmons is informed of this event by a Vagan officer. Simmons reacts to this news by panicking and leaving his post, commanding the Vagan officer to take his position for him. Simmons makes his way to the escape craft hanger and is stopped by two Vagan soldiers, which he shoots in an attempt to escape. As he boards the craft he is attacked by one of the dying Vagan soldiers who he had shot.
He eventually escaped the base after it fell to the Federation forces and called out for aid. He is met by Fram Nara in her xvb-fnc Fawn Farsia. Fram Nara informs Simmons that she knows about his murder of the two Vagan soldiers and tells Simmons that he is not worthy to be on Zeheart's ship. Fram then destroys Simmons's emergency escape craft, killing him in the process.