Stuff I found out when I'm making my own set of combat challenges:

• Targets must be under the "Empty" GameObject called by the mod. You can use the same custom map for sandbox and mission, but you'll need a separate version for each if you want both to have targets.
• Ships must have 0 HP to be considered killed. A destroyer struck with 3 Infernos will sink, but it still has HP and is therefore still "alive" by SP script logic. (You may encounter this if you played the original Combat Challenges by NathanMikeska) Luckily destroyers don't sink all the way in my map so I can find this
• You can install laser defenses and missile launchers on ships, but they will separate from the ship if the ship sinks, and will cause moving ships they're mounted on to turn. If you make a missile boat, it must be stationary.

So yeah wasted a few days lol, all my added scripting is confirmed working, combat challenges documentation from me maybe... eventually

Shooting the mast of a "sunken" destroyer

Wonder if I'll need to mark NathanMikeska as a contributor, since I used the original Combat Challenges code as a base