Improved Jump Jet
A modern refinement upon the centuries old design of standard jump jets, improved jump jets are twice as large and as heavy as their normal counterparts, but can propel a 'Mech further with less heat build-up.
Developed by Clan Wolf-in-Exile in 3069,  thanks to their sharing of the specs with allies of the Arc-Royal Defense Cordon fighting against the Blakists and the espionage efforts of their Crusader brethren, they have spread throughout the Inner Sphere.
- TechManual, pp. 225-226, Improved Jump Jets