The Cohors Arma is the largest and most structurally complex Branch, subdivided into three permanent operational divisions, each commanding a distinct domain of warfare:
- Classis Navalis — Fleet Operations: capital ships, carriers, destroyers and their escorts.
- Ala Volatilis — Fighter and small-craft Operations: fighters, gunships, interceptors, bombers, electronic-warfare craft.
- Legio Terrestris — Ground and Boarding Operations: marines, boarding parties, ground assault.
All three divisions use the same horizontal rank ladder. Divisions are operationally independent but coordinate under the Praetor Armae (Director) and the Praefectus Armae (Branch Commander). For joint operations, a Centurio Operationis is appointed to coordinate across divisional lines.
Commands all capital-ship and large-hull operations: carriers, battlecruisers, destroyers, frigates, and their escort complements. Organised as a fleet (Classis) composed of task groups (Agrupamenta), each centred on a capital ship (Navis Capitalis) with its escorts.
Unit structure
- Fleet (Classis) — all ships of the Branch — Praefectus Classis.
- Task Group (Agrupamentum) — 1 capital + 2–4 escorts — Centurio (senior Trierarchos).
- Capital Ship (Navis Capitalis) — Centurio — Trierarchos.
- Escort Hull (Navis Praesidii) — frigate / destroyer class — Centurio — Gubernator.
- Department (Departamentum) — Decanus.
- Watch / Post (Vigilia Navis) — 2–4 personnel — senior Miles.
Shipboard departments
- Gubernaculum — Navigation: helm, QT navigation, plotting.
- Armamentarium — Weapons: turrets, torpedoes, ordnance.
- Machina — Engineering: power, propulsion, damage control.
- Scutum et Bellum Electronicum — Shields and electronic warfare.
- Valetudinarium Navis — Shipboard medical (triage and emergency).
- Portus Alius — Flight Deck (carriers only): launch, recovery, hangar.
Commands all small-craft operations. Organised by Wings (Alae), each composed of Squadrons (Squadri), Flights (Volatus), and two-ship Elements (Elementa).
Unit structure
- Wing (Ala) — 2–4 Squadrons — Praefectus Alae.
- Squadron (Squadro) — 8–12 craft — Centurio — Decurio Squadronis.
- Flight (Volatus) — 4 craft (2 Elements) — Decanus — Decurio Volatus.
- Element (Elementum) — 2 craft — Miles senior.
- Individual craft — Miles — Eques Caelestis.
Craft specialisations
- Eques — Fighter (space superiority): intercept, dogfight, escort.
- Sagitta — Interceptor: high-speed intercept, point defence.
- Ballistarius — Bomber: anti-capital strike, torpedo delivery.
- Navis Armata — Gunship: close support for ground operations.
- Navis Electronica — EW Craft: jamming, signals intelligence, electronic suppression.
- Explorator Levis — Recon (Ala-attached): fast tactical reconnaissance.
Commands all ground engagements, boarding actions, and shipboard assault. Organised as a Legio (whole ground force), composed of Cohortes (battalions), which contain Centuriae (companies), which contain Contubernia (squads).
Unit structure
- Legion (Legio) — all ground forces — Praefectus Legionis.
- Cohort (Cohors) — 3–4 Centuries — Centurio Cohortis.
- Century (Centuria) — 3–4 squads (~30–40 marines) — Centurio Pilus Prior.
- Squad (Contubernium) — 6–8 marines — Decanus — Optio Manipuli.
- Fire team (Scutum) — 2–4 marines — Miles senior.
Marine specialisations
- Miles Impetus — Assault Marine: breaching, close-quarters combat.
- Miles Transcensor — Boarding Specialist: ship/station entry, EVA assault.
- Miles Gravior — Heavy Weapons: suppression, anti-vehicle, area denial.
- Miles Explorator — Reconnaissance: ground scouting, pathfinder.
- Miles Faber — Combat Engineer: breaching charges, fortification, repair under fire.
- Miles Medicus — Field Medic: front-line triage (attached from Cohors Medicina).
Most Republic combat operations involve more than one division. The following coordination rules apply:
- Joint operations are commanded by the Praefectus Armae (Branch Commander) unless a specific Operation Commander (Centurio Operationis) is designated by the Praetor Armae.
- Air support for Legio — the Praefectus Alae detaches Decurio Volatus-level flights under temporary attachment to the Centurio Cohortis for the duration of the ground operation.
- Marine ops off a carrier — Legio units aboard carriers answer to their own Centurio Cohortis, not to the Trierarchos of the carrier. The Trierarchos retains authority over the ship; the Centurio Cohortis retains authority over the marines.
- EW and fighter escort for Classis — Ala elements assigned to fleet protection answer to the Praefectus Classis for tactical direction but to the Praefectus Alae for internal matters.
Embedded Commissariat
Each divisional-level command (Classis, Ala, Legio) has an embedded Commissarius assigned by the Commissarius Primus via the Praetoria Fidei. The Commissar attends all planning sessions, may address any member on doctrinal grounds, and reports directly to the Holy Office — not through the divisional command chain.
Cross-division rank equivalence
A Centurio of the Classis Navalis holds equivalent rank to a Centurio of the Ala Volatilis and of the Legio Terrestris. Cross-division authority is conferred only by the Praefectus Armae or the Praetor Armae for a defined operational scope.
Glossarium
- Classis Navalis
- Fleet — capital ships and escorts.
- Ala Volatilis
- Wing — fighters and small craft.
- Legio Terrestris
- Legion — ground forces and boarding parties.
- Trierarchos
- Capital ship captain (Centurio rank).
- Decurio Squadronis
- Squadron leader (Centurio rank).
- Pilus Prior
- Century commander (Centurio rank).