Caisson
Caisson is a reinforced hull that is used in Arctic Submersible rig. In winter, ice blocks tend to flow with the ocean current and apply enough force to damage the jack up legs or barge hulls. Hence reinforced hulls called "Caisson" are used with arctic submersible rigs. The rig is towed to location when the sea is ice free and Caissons are submerged into sea bottom to allow uninterrupted operations even with ice flow.