Why Royal Navy carriers carried substantial gun batteries

Were aircraft carriers supposed to engage targets with their own guns?

Yes. Royal Navy carriers fired at aircraft, Unicorn carried out bombardment, and their 4.5-inch batteries impressed some American observers.

Royal Navy carriers used their own guns against aircraft that came within range. Formidable is cited as a carrier that fired its guns, while Unicorn is singled out for bombardment. Some American observers regarded the British fleet carriers' 4.5-inch batteries as substantial enough to look intended for surface engagements. That impression is distinct from the examples of actual anti-aircraft fire and bombardment.