They were built at the low water mark with the intention that they would be hidden at high water, ripping a hole in any landing craft or LVT hitting the obstacle.
Prior to a landing, US Navy Underwater Demolition Teams (UDTs) were deployed to destroy these obstacles and could be destroyed with demolition charges.
These models depict obstacles that could not be destroyed before the landings started.
Dimensions: (Without angle iron)
Height 25mm, Diameter 40mm (All dimensions are approximate)