Resin Model Kit. The FV 621 Stalwart, known as the 'Stolly' is an amphibious truck in service with the British Army. Developed by Alvis it was introduced in 1966 as a general transport truck. It comes from the same line as the Saracen, Saladin and Salamander. The Mk 2 has a two man crew with room for a third seat. It can carry 38 fully equipped troops and features a more powerful jet drive unit giving it a faster speed in water. The windows have been modified too, to improve visibility.