For anyone who has read orion fleet, maybe something along the lines of that universe's stealth system. The ship itself uses a system that puts it partly out of regular space. The stealth system has high energy drain, meaning no shields while in use. Stealth in that universe also works both ways. While it is engaged a ship is more or less blind to the outside world except for detecting gravity disturbances (large artificial sources, asteroids, planets, anything big really). You would be unable to track small ships, tell if another ship has shields/weapons armed, or even aimed at you. Stealth units and FTL (which both use wormhole like physics to function) both require mass and energy to be used efficiently in Orion Fleet as well, so small ships can't really fit the system but huge ships cannot either since the power drain is like being in constant FTL (so no super big cloaked ships). This means stealth ships would be in a middle ground, not fast but not heavily armored and generally with a few heavy hitting weapons only. (Sorry this is a little messy, short on time)