Arbor Arms is working with Aqualung to offer a low cost retrofit kit for armor carriers so that they can be used in conjunction with Aqualung Buoyancy Compensators. In this case, we see the Calypso.
The cummerbund is elastic so it will allow a buoyancy compensator or horse collar to still inflate yet keep your gear nice and snug.
Additionally, the Aqualung weight belt is worn with ditchable weights fore and aft to keep them out of the way of holsters and magazine carriers.