They must have gone days or weeks at a time with no combat missions to fly - or at least, very few (e.g. combat air patrols).
So considering there must have been dozens of them on each ship, just eating up supplies, what were they used for when they weren't being pilots?
Or are my assumptions wrong?
What pilots did when they weren't flying depended on where the ship was. If the ship was in a combat zone, but not actively fighting, they were typically standing ready to fly. If the ship was outside areas where combat was likely, they would be doing a mix of training, paperwork and resting.
When a British carrier was in a combat zone, pilots who were not actively flying would be ready to fly on fairly short notice. It was not uncommon for some pilots to be on scramble alert, sitting in their planes on the flight deck, ready to launch immediately when reports of enemy aircraft came in. This was only done when there was a significant threat of air attack, as it was not particularly comfortable for the pilots and took up space on the flight deck that might be needed for other aircraft. Other pilots, just about to fly, might be receiving a briefing in the ship's briefing room. This would lay out plans, tactics and rendezvous locations, as well as radio frequencies and so on. Again, this was only really necessary in some circumstances, when a strike or CAP was being prepared. Instead, most pilots were in resting spaces that were convenient to the flight or hangar deck, so they could be ready to launch quickly. Typically, this was the wardroom, the officer's dining room/club. When the carrier Illustrious was bombed in January 1941, there were severe casualties amongst the ship's pilots, as a bomb had detonated just above the wardroom. When Eagle was torpedoed in August 1942, fighter pilot Mike Crosley had just been served some soup in her wardroom - 'My soup plate flew up and hit me in the face — and all the lights went out.'
When the prospect of action was slim, pilots had a variety of duties. Training was constant, with pilots practicing their usual flying skills as well as more complex tactics. It might involve actual flying, or just be paper exercises. Exercises could include simple repeated take-offs and landings, simulated air-to-air combat against other aircraft or against towed targets, navigational practices, or simulated attacks against other ships in the fleet or shore targets. This might involve other services too; it was not uncommon for shore-based RAF units to attempt to attack RN carrier groups. This gave the RAF practice in attacking ships at sea and the Fleet Air Arm pilots a chance to practice defending them. When British carriers went into port for repairs, refits or resupply, their squadrons would typically move to land bases nearby. This allowed them to continue their training routines, as planes could not easily fly from carriers in port due to the lack of headwind over the deck.
Paperwork and administrative duties were also common. Fleet Air Arm squadrons included not just the pilots and other aircrew, but also the maintenance staff responsible for maintaining the planes. A squadron's pilots had a leadership responsibility for these men. A squadron's ratings (enlisted men) would be divided up into several 'divisions' of 10-20 men, each with a pilot (or other squadron officer) in charge of them as the divisional officer. The divisional officer was the main point of contact between the ratings of his division and the RN's bureaucracy. He was in charge of their service documents, for recommending them for training courses, and for representing them if they ran into trouble with naval law. Other pilots might have other duties within the squadron, secondary to their role as pilots. The squadron's Senior Pilot was responsible for overseeing the training of the squadron's pilots. The Maintenance Officer ensured that the squadron's aircraft were kept properly maintained, while the Armaments Officer ensured that their weapons were cared for. The Maps and Charts Officer kept charts up-to-date, and the Diary Officer was responsible for recording the squadron's operations. Pilots themselves had to fill out paperwork too. Each pilot had a log book which had to be updated after each flight. There were intelligence forms for sightings of enemy aircraft, forms for claiming and confirming kills, and the notorious A25 form for reporting damage to an aircraft.
Finally, pilots spent time resting and recuperating. A squadron typically had more pilots than it had aircraft. This made it easier to replace casualties, and let the squadron rotate pilots to ensure that fresh pilots were always flying. Off duty pilots aboard ship would typically be resting either in their cabins, in the wardroom or watching planes land on the flight deck, just eating up supplies. If the ship was out of combat, then there were far more options to relax. Sports were common, as were films, books and music. The wardroom had a bar where pilots could relax. When the ship was in port, the opportunities available to off-duty pilots were much less limited, though it did depend on the port.