M-3: multi-Mach Maglev transport in sub-surface ocean tubes

Development of Maglev (magnetic levitation), a new mode of transport in which high speed vehicles are magnetically levitated and propelled along a guideway, began in 1966 with the invention of superconducting Maglev by Powell and Danby. Since there is no mechanical contact or friction, the speed of Maglev vehicles is only limited by air drag. In the atmosphere, the practical limit is about 500 kilometers per hour (~300 mph). In low pressure (e.g., 1 torr or less) tubes or tunnels, speed is only limited by the straightness of the route, and the distance between stations, with the need to accelerate and decelerate. Tunnels are generally too expensive, 30 million dollars per mile or more, to be practical for most Maglev routes. However, undersea tubes have the potential to be lower in cost, and can provide intercontinental travel at speeds of thousands of miles per hour