The O-Type is the Isan’s heavy utility module, with thick armor and sections with enough space to house a small battery of heavy turrets, a hangar, or a Nephelium torpedo launcher. O-Types look like filled donuts, with couplings on either side to stack up and connect to a command module. Each O-Type is itself made from four wedges, each taking up a 90-degree arc of the ship. These wedges are swappable, allowing crews to configure O-Types as pure turret, carrier, or torpedo modules or to use some combination of the three. O-Types can spin independently from the command module or the other modules in the stack, allowing mixed-function O-Types to point their sections in the right direction regardless of what the rest of the ship is doing. While O-Types have their own engines and thrusters to operate independently of command modules when necessary, they’re not designed to operate wholly independently because they lack a full-scale Nephelium drive, requiring a command module for faster-than-light travel or to power high-energy Nephelium tech. (O-Types have miniature Nephelium reactors, but they’re mostly used for artificial gravity and other basic applications.) As a building block for ships, O-Types emphasize armor and firepower at a cost of speed and maneuverability. The more a ship is expected to “tank,” the more it’s going to use O-Types over X-Types. 

O-Types come in a variety of sizes, but the most common ones are also the largest, at about 80 yards in diameter and 20 yards tall. Like other Isan ships, its decks are concentric circles with gravity pointing away from the ship’s central axis. A full-size O-Type has six concentric decks, not including the core at the center that houses the ship’s engine, couplings, and power/data rail. Each O-Type consists of four detachable wedges, each in a 90 degree arc. (This happens before a battle: Wedges can’t fly independently of the O-Type, making combat reconfiguration impractical.) The bulkheads between the sections allow crew to escape into adjacent ones in case a section is damaged or boarded, and these can be vented to put out a fire or launch a boarding party into space. O-Types also have doors on the top and bottom, allowing crew to move between O-Types or other modules in a stack as long as these doors are lined up. There are several kinds of O-Type wedges equipped for specializations like minefield deployment or deep scanning, but by far the most common are turret banks (heavy or light), hangars for launch craft, and Nephelium torpedo systems. For turret banks, Isan ship designs use a Nephelium-boosted firing system, which allows for more power and accuracy with a smaller barrel design, and weapons engineers can increase or decrease the Nephelium boost by drawing power through the rail from other ships in the stack as needed. (The drawback is that these turrets are less effective when the O-Type isn’t connected by rail to a command module’s Nephelium drive and has to rely on its own mini-Nephelium reactor.) Hangar wedges are set up to “drop” launch craft into the battlefield: Because the O-Type’s internal gravity has down pointing to the outside of the ship (like a centrifugal force), it can hang launch craft like bats, then when it opens the hangar bay doors, the clamps release and the launch craft “fall” out of the hangar and into space. When launching, hangar wedges draw extra power if available to increase the g-forces of the artificial gravity to accelerate the launch craft even further. Torpedo wedges fire Nephelium torpedoes, which seek targets “painted” by a Nephelium particle gun that’s built into the wedge. This is the only type of guidance system that works in space in the Conflux, because the Engine Star’s radiation fries other types. (Normal missile guidance systems still work planetside or inside ships or stations.) The Nephelium crystals used in the guidance system also amplify and shape the explosion, allowing for a compact projectile that can cause significant hull damage even against heavy armor.

O-Types are key to the Isan’s histagal doctrine because they allow Isan admirals to construct cruiser- and carrier-like ships based on the needs of each engagement. Attaching several O-Types to a command module gives it the firepower of a destroyer or the carrying capacity of a light carrier, several more make a cruiser or full carrier, and a command module with multiple large stacks of O-Types can serve as a battleship or heavy carrier. In most Isan battle groups, the “screw” configuration—a screwhead-shaped D-Type with a stack of some number of O-Types resembles a screw floating in space—was the most common heavy ship format, the workhorses of the Isan Free Navy. But O-Types were also important for hardening the other, more specialized command modules, beefing them up with additional firepower and launch craft as needed. Because O-Types can fly independently, they also can reconfigure in battle as friendly modules take damage. Each O-Type is sturdy, and often even a critically damaged ship will have undamaged modules that can detach from the stack and link up with another allied ship that’s still combat-worthy. An Isan ship isn’t truly destroyed until all its component modules are disabled: A Feron ramming attack that would cause a massive hull breach on a Malleon ship would only destroy a few O-Types, allowing the Isan ship to jettison them then link the undamaged modules in the stack right back together for a counterattack.