The Tactical Weapons Module (TWM) is located on the "roll bar" of the ship. It houses the Phaser Cannon and a Torpedo Launcher. The (TWM) is just one of many possible "Roll Bar" modules that can be attached at any major Starbase. This module It contains 8 PhotonTorpedo Launchers. It has 450 Photon Torpedoes and 12 Tri-Cobalt Devices stored.
The Habitat Module is used when transporting colonists or troops. It has room for 500 people and their belongings.
The Cargo Module is just that. It is big and bulky, but it adds and extra 100,000 metric tons to to cargo capacity of the ship.
For special operations, this small module is attatched. It has quarters for 50 people, negotiating rooms, and a small entertainment center. It is designed to be a neutral area where negotiations can be staged.
This is essentially A third Warp Nacelle with its own M/ARA and power supply. This supplements speed when you need to get somewhere far away fast.
The Module itself is nothing more then a big bundle of sensors with a hull and connects Gamma welded to it. It makes a science ship's sensor array look like a tricorder.
This unusual module is used in conjuction with other Starships. During a rescue operation, the most common cause of death while awaiting rescue is failure to transport fast enough from the Hazard Area. So, if needed, the Akira Class can beam over 30,000 persons an hour with this module. It runs off its own power supply, so other ship systems won't be affected.
This is a very mission-specific module. It has room for 300 Ground Troops, a command HQ, and a subspace relay with Starfleet Command.
This very useful module is a completely sealed off hospital. It has operating rooms, and ICU, medical labs, and it all runs off its own power, thus minimizing the risk of spread of infectious disease.
A heavily armored module in itself, it includes extra shield generators, and metaphasic shield generators, thus insuring the ship con go almost anywhere freely.