Hi Pilatus
Whilst it's true that you'd get a "return" from using a weather radar to "paint" an aircraft, don't forget that a weather radar is a relatively crude device and will show returns from a lot of things, such as coastlines, tall buildings, outlines of rivers, large masts, big steel objects like ships and lots of indiscriminate clutter.Proper air-to-air radars, such as fighter radars are designed to be much more discriminate and to be less of a blunt instrument and will be able to track multiple targets and scan for more targets. Using a non-specific radar such as a weather radar for tracking ships is pretty crude.Also, you wouldn't use one for a let-down procedure because it's too risky.The Casa's belly radar is miles ahead of the simple radar in the King Air.
regards
GttC