XXL fusion engine

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The XXL fusion engine, also known as XXL, Double XL, or (more formally) extra-extralight engine, is an advanced and experimental fusion engine type.


The XXL engine weighs one-third as much as a standard fusion engine, but with some significant drawbacks in its present form. The XXL's light but bulky shielding technology takes up twice the space in side torso sections as an Inner Sphere or Clan XL engine of similar output, is five times as expensive as a comparable XL engine, and—most crippling—produces greatly increased heat. Due to the engine shielding shaved down to the bare minimum for safe operation, waste heat is produced at all times, even when the reactor is not powering the vehicle's movements or other energy-demanding systems; equivalent amounts of heat are doubled when actively propelling a BattleMech.[1][2]


Since the revolutionary development of the XL engine back in the original Star League era, engineers continued to try to push the envelope in further reducing the overall weight of a fusion engine, with the ongoing conflict between the Inner Sphere and Clans powers providing further impetus to such efforts. Clan Diamond Shark was recognized as the modern originator of that culture's XXL fusion engine as of 2954, while the Federated Commonwealth succeeded with a different approach in 3055. Current employment of fusion engines suggests the engine is not widely accepted for practical use.[2]


  1. Maximum Tech, p. 58
  2. 2.0 2.1 Tactical Operations, p. 309, "XXL Fusion Engine"