Towards the end of the First Great War and through the Interwar Period, experiments were made with a new type of vehicle: The armoured personnel carrier. This new type of vehicle provided the infantry with mobility and armour similar to a light tank and opened new tactical and operational possibilities. Nevertheless, it was not until the Second Great War that massed formations of APCs were deployed, starting with the elite motor rifle divisions of the Asugisalic army. At the same time, many nations were concerned about the vulnerability of large armoured formations to poison gas attacks. These fears were confirmed when forces loyal to the Erilaz Muha released poison gas at a gathering of forces loyal to King Humli in the port town of Veisafjǫrðr, killing thousands of innocent civilians and starting the Asugisalic civil war. Despite the subsequent Treaty of Valhǫll banning such weapons, overpressure systems became standard on all armoured vehicles from that point on. Throughout the 1950s, the Usonian Technate experimented with various designs for APCs, culminating in the adoption of the M61, named for the year of its adoption. Thanks to its innovative aluminium hull, the M61 provided excellent mobility, combined with amphibious and airdrop capabilities. The vehicle achieved iconic status during the Third Great War, where it was ubiquitous on all fronts.