Grim Reaper is a stealthy resurrection submarine. They are not visible to units on the surface if your enemy doesn’t have sonar nearby. Use them as support to provide repairs, reclaiming and resurrecting wrecks. They are relatively cheap and provide essential support to your navy maneuvers, don't forget to mix them in your fleet. Don't forget however the high energy cost of building and using them.
Resurrecting requires 50% of unit's energy cost.