The variable fighters were the highly adaptable, transforming battle mechas designed by the Cardax Motorworks. They were capable of both ground-bound missions and air support roles, altering between the assault walker mode and the fighter mode.
That technology had been invented in the second half of the 31st century, but it had to be developed further to become of real use. Eventually, first fully operational variable fighters were built in the 3010s, with the Wyvern-class battle mecha being the first successful, intermiedate model of the line. It was actually a regular, but sleek and relatively light battle mecha with impulse engines and retractable wings, which allowed it to fly in a semi-controlled manner. Variable fighters had been improved further, though, and much more advanced model, Icarus-class variable fighter, capable of space flight, was introduced in 3145, at the beginning of the New Machine Purge.
Behind the scenes
The idea of Wyvern and Icarus-class vehicles was inspired by the Viking of StarCraft, APUs of Matrix and variable fighters of the Super Dimension Fortress Macross.