TR-3B Anti-Gravity Spacecrafts.

“It doesn’t exist officially.” It uses highly pressured mercury accelerated by nuclear energy to produce a plasma that creates a field of anti-gravity around the ship. Craft can perform all manner of rapid high speed maneuvers along all three axes.

http://www.military.com/video/aircraft/military-aircraft/tr-3b-aurora-anti-gravity-spacecrafts/2860314511001