Why four listed carriers meant one available ship

HMS Hermes was in a major refit that included fitting her ski jump, while Illustrious and Ark Royal were still being built or laid down. HMS Bulwark had been withdrawn six months earlier than intended, removing the force's temporary cover. The newly entered HMS Invincible was therefore effectively the only available carrier even though four ships appeared on the books. Invincible was also new enough to be working through the normal quirks of entry into service. Headline fleet totals could conceal severe readiness constraints.