Comment by stetrain

ULA calls this "SMART reuse" but has not yet successfully achieved it with their Vulcan rocket.

https://planetary.s3.amazonaws.com/web/assets/pictures/_2400...

In some ways this is simpler, but in others it is more complex since you need a way to catch the engines before they dunk in the salt water. A rocket booster that is already set up with avionics, engines, and fuel can guide and land itself without needing a precise helicopter catch etc.