Non-rigid airships are often called "blimps". Non-rigid airships, often called "blimps", rely on internal pressure to maintain their shape. WAMI sensors are typically mounted on manned airplanes, drones, blimps and aerostats. Today, familiar gas balloons include large blimps and small latex party balloons. Airship Management Services owns and operates three Skyship 600 blimps. It is unlike both the original Zeppelins that had a rigid skeleton and non-rigid blimps. The Navy's forces were expanded to include seaplanes, submarines and blimps. Simulations have ranged from blimps, commercial and military aircraft to the Space Shuttle. Later, more advanced blimps with purpose-built gondolas were used. The Connecticut Aircraft blimps were powered by Hall-Scott engines. The most iconic of these are the Goodyear Blimps. The Goodyear blimps are still a common sight in the USA. Skycruise Switzerland AG owns and operates two Skyship 600 blimps. Goodyear granted the film use of all three of its U.S.-based blimps for "Black Sunday". One was sunk and several probably damaged by bombs dropped by the blimps.