- Weight: 18.3 t
- Length: 7.33 m
- Width: 2.98 m
- Height: 2.37 m
- Crew: 3 + 10 passengers
- Main armament: 1x Gabha G-116 30mm Revolver Cannon in turret
- Secondary armament: smoke grenade launchers
- Engine: liquid-cooled diesel, 320 hp
- Suspension: 6x6
- Operational range: 800 km
- Speed: 105 km/h, 10 km/h in water
Amphibious, low profiled, silent - Sionnach.
Domestically produced during the 70s, this APC was produced for the SDF-Army. It is capable of anti-aircraft defense, has amour-penetrating ammunition and strong enough armour to withstand many things. It replaced the Faolchú Armoured Personnel Carrier.
Several versions of the Sio-I exist as well, most of them with technical aspects differing, their number increasing with the successor being introduced. These versions are:
- Sio-I Mortar Carrier: Replaced the turret and the troop compartment with a Mortar, Heavy, Model 1961 for heavy fire support to the infantry as part of the mortar batteries.
- Sio-I Ammunition Vehicle: Ammunition carrier for the aforementioned mortar carriers.
- Sio-I Mobile Command Post: Slightly raised roof and more radios, but no armament, used for command and control, including the direction of artillery and air forces.
- Sio-I Rocket Launcher: Replaced the entire troop compartment with a Feadán Fe-21 Mark III MLRS, only prototypes.
- Sio-I Recovery Vehicle: Armoured recovery vehicle for tanks and other vehicles. Can be used as a tug.
- Sio-I Engineer Vehicle: No armament except for a heavy machine gun, but with an hydraulic excavator arm, winch and a dozer blade.
- Sio-I Field Ambulance: Unarmed field ambulance or foundation for a field ambulance.
- Sio-I Power Generator: Sio-I disarmed, but with a power generator and a larger fuel tank, only prototypes.