Hydrofoils with surface-piercing foils have been around for a century. They work well on a flat calm lake, but pitch and roll like any other ship in a choppy sea. The idea of a submerged foil, less affected by the waves, was first developed by the English engineer Christopher Hook. Stuck in Kenya during World War II, he stripped the wreckage of a Walrus seaplane to build an experimental hydrofoil on Lake Victoria. It flew level by using skis fitted to hinged arms at the bow to sense the water surface and control the angle of the submerged foil. After the war, he built several small ‘hydrofin’ craft, which he sold as pleasure boats.
Although Hook’s invention was largely ignored in the UK, it soon got attention from the US Navy. By the late 1950s nuclear submarines could run submerged at more than 30 knots. No surface warship could keep up, and the Navy needed a fast submarine tracker which could operate in rough weather. As the hydrofin’s mechanical skis and linkages were vulnerable to damage, the Navy experimented with an internal control system using gyroscopes from aircraft autopilots to drive hydraulic controls.
The result was as much aircraft asin 1960. USS was 35m in length, and could reach speeds of 48 knots. Her forward foil was used for steering, and the larger aft foil supported four propellers driven by shafts running down the struts.
