Just need some verification on Gunnery Attack Activation

So, I had a demo game that I organized for friends using the USS North Carolina (plus a few Fletcher-Class Destroyers) vs. the HMS Prince of Wales and HMS Repulse (Pretty much Task Force Z).

I managed to already ranged in with my Prince of Wales on the USS North Carolina and score 4 hits out of 6 RoF (4+ to Hit since I'm hitting a Target Score of 4 in between 20 to 60 cm and there's no cover and he has opted not to carry out evasive maneuvers). Hit Location was the 18, the Primary Weapon Systems. He just needed a 3+ for the armor save. He failed 3 of them thus the 3 hits caused 9 damage which then resulted in the USS North Carolina losing all of her main guns and took 9 hull damage.

May I verify that the Gunnery Attack Activation above was done correctly?

Hello Zenai2020 and thank you for asking clarifications.

Two things were played wrong in the example you mention.
1. The damage multiplier is applied before armor is rolled. So the 3 hits would require 9 armor rolls.
2. The 18 hit location will only destroy one weapon system (if 6+ armor rolls have failed). Each entry on the datacard is a separate weapon system. So North Carolina has two primary weapon systems, the front guns and aft guns. It would only lose one of those, not both.

Keep on gaming!