Are Shields Worthless against AN Attacks

[JonBrave]

Thanks a lot, guys, for making it yet more complicated...

For those who feel like being kind enough to answer (please don't refer me to another thread):

1. Shield has (a) defence and (b) protection
2. There is (a) melee and (b) missile combat

I make that 4 combinations. Which ones do/don't work against AN damage (weapon?). I'll even accept "Mostly"/"Hardly" for "Yes"/"No", if required.....