HMS Illustrious, like many modern carriers, has its own form of self-defence. It has a Goalkeeper Close-In Weapon System anti-missile turret, and two GAM-B01 Okerlikon 20mm close-range cannons.
HMS Illustrious carries 22 aircraft at a time when in one of its two roles:
- When in the strike, anti-sub warfare and anti-surface warfare role, it carries 12 AV-8 Harrier GR.7/9s, and ten helicopters in a combination of W-101 Merlin and WS-61 Sea Kings.
- When in the strike and anti-sub warfare role, it carries 18 Sea Harriers and four helicopters.