On November 18, 1991, O'Neill filed a patent application for a vactrain system. He called the company he wanted to form "VSE International", for velocity, silence, and efficiency. However, the concept itself he called "Magnetic Flight". The vehicles, instead of running on a pair of tracks, would be elevated using electromagnetic force by a single track within a tube (permanent magnets in the track, with variable magnets on the vehicle), and propelled by electromagnetic forces through tunnels. He estimated the trains could reach speeds of up to 2,500 mph (4,000 km/h) — about five times faster than a jet airliner — if the air was evacuated from the tunnels. To obtain such speeds, the vehicle would accelerate for the first half of the trip, and then decelerate for the second half of the trip. The acceleration was planned to be a maximum of about one-half of the force of gravity. O'Neill planned to build a network of stations connected by these tunnels, but he died two years before his first patent on it was granted.