Idea - booster.
Component, that is basically an engine, that can be put in addition to normal engines and can be turned off to not affect fuel usage, but is stupidly ineffective, like 3x fuel consumption.
Idea is, this component can be mounted on warships to make them rather fuel efficient when not in combat, but have good speed when in combat.
I know I can do this with tugs or carriers, but it would be great for patrol ships, tat needs some combat power, while being cheap to produce.
To make it even less attractive to put on every warship it could be able to overheat (get destroyed) after some time of constant usage.
For programming simplicity it could be created, that it isn't throttable (I don't know if this is right word. It's used in KSP in this context) i.e. It can either be turned off, or work at 100%. It couldn't be able to be set to other values, like 50%.