They operated inside vactrain tunnels and ran at hundreds of miles per hour.

During the 1970s, he advocated the vactrain high-speed transit concept.

Studies of commercial feasibility reached differing conclusions and the vactrain were never built.

A vactrain (or vacuum tube train) is a proposed design for very-high-speed rail transportation.

The only real constraints on a vactrain system are: 1) the need to place the tube, and 2) the need to keep the track straight.

In a vactrain system, a magnetically levitated train moves through a vacuum sealed tube.

ET3 Global Alliance (not a 'vactrain', but a similar technology)

Evacuating the atmosphere to make it a vactrain would eliminate this drag but would require additional power.

For further information see Vactrain and Hyperloop.

Mr Musk has denied it will be a so-called "vactrain," a concept that is already being pursued by a company in Colorado.

Swissmetro was a futuristic Swiss national transportation project using vactrain technology that went into liquidation in November 2009 because of a lack of support.

The ultimate solution is likely to be a vactrain, also known as Evacuated Tube Transport or ETT.

Swissmetro: An earlier project, Swissmetro AG envisioned a partially evacuated underground maglev (a vactrain).

Later, vactrain appears in the story "Mercenary" by Mack Reynolds published in April of 1962, where he mentions Vacuum Tube Transport in passing.

The Hyperloop is thus a mixture of maglev train and pneumatic railway (the concept is a modified version of the "vactrain" - using evacuated tunnels as low-resistance conduits for ultra-high-speed trains).

The vactrain concept theoretically eliminates these obstacles by employing magnetically levitating trains in evacuated (airless) or partly evacuated tubes or tunnels, allowing for theoretical speeds of thousands of miles per hour.

However, closer examination shows that the many papers published at SWJTU never use the term vactrain, and instead refer to the ETT work of Oster, Zhang, and Wang.

The "vactrain" concept was floated in the early 1910s and a paper written by physicist R.M. Salter and published by the Rand Corporation in 1972 titled the "Very High Speed Transit System," or VHST, describes something very similar to what ET3 is developing.