Semi-submersible marine craft

A semi-submersible craft 1 comprises a vehicle housing 2, a propulsion means 3 connected to the housing, and a strut 4 extending from the top of the housing, the vehicle being adapted to have sufficient buoyancy such that it maintains the vessel housing at a predetermined level under the water with the strut extending out of the water. The housing may be formed from two or more hulls joined together while an engine 6 for driving the propelling means may be mounted at the top of the strut above the water. Fins 8 and a keel 5 may be provided to maintain the strut in a substantially vertical orientation. The front of the craft may include a detachable nose cone 7 accommodating sensing equipment while means to control the craft may be contained within the strut or the housing.