Fusion Engine - Compact
A Compact Fusion Engine is similar to a Fusion Engine, but utilizes denser radiation shielding and other features to reduce the engine's volume by half. There is a weight penalty for the density; compact fusion engines are 50% heavier than the standard fusion engine, limiting its use to 'Mechs that require a lot of internal space and/or have tonnage to spare. One benefit of this arrangement is that penetrating hits are less likely to hit the smaller profile of the compact fusion engine than they would a bulkier standard fusion engine.
- TechManual, p. 214