masted ships in its earlier  years, the entire stage was jacked up while steel and concrete  pilasters were built underneath the structure for added support,  doubling the stages height after the new foundation was poured. Its  floor is retractable to reveal a deep flotation tank as well as  windowed camera cabins for underwater filming. In "The Great Race,"  a portion of the gradually "melting ice floe" was attached to cables  that kept the slab of "ice" in position and the portion which  gradually gave way underneath Professor Fate was pulled down by an  underwater diver in the tank.