Go back and read some of the material on the Armoured carriers website.
The Royal Navy’s first armoured flight deck aircraft carrier HMS Illustrious had been active a mere six months when her design and construction was put to the ultimate test.
Illustrious had 15 Fulmars aboard, but on the morning of 10 Jan 1941 only 12 were serviceable (not clear if any more became serviceable that morning). They had many radar contacts that morning but these were shadowers. Experience had shown if you could down the shadowers it helped to at least delay the attacks if not prevent them altogether while the enemy located you. So the CAP had been chasing these. One shadower was shot down at 0930. By 1120 there were 5 Fulmars airborne which intercepted and shot down another SM79 shadower. One Fulmar lost its canopy and had to return to Illustrious. So then 4 airborne of now maybe 11 serviceable.
1220 first attack comes in. Radar detected them at 6 miles. Why? Because they were TB coming in low under the radar horizon. Of the 4 Fulmars on CAP, Red section (2 Fulmars) expended their ammo on these (they were due to land at 1245 anyway at the end of their time on CAP). The second pair had also been drawn down low by this attack and had expended some of their ammo attacking enemy aircraft seen parked on the Italian Airfield on Linosa island as they flew across it while giving chase.
1225 second raid detected on radar at 28 miles. This was the first appearance by Fliegerkorps X. 4 airborne Fulmars sent to intercept but had to climb from low level.
Illustrious had 4 Fulmars already on deck scheduled for take off at 1235 as the replacement CAP. 1230 Captain requests fleet change course to launch them (necessary to keep fleet together and protected from air and submarine threats). Delayed until 1234. Additional 2 Fulmars (only 3 available at that point, although one pilot believed 6 others were serviceable at that point) had to be brought up from the hangar to be readied on the flight deck. Then 1 went U/S and only 4 got off before the bombs started falling.
1235 enemy aircraft sighted at 12,000 feet.
1237 last Fulmar leaves the deck. Now 8 airborne, 2 without ammo and reduced to making dummy passes. 6 climbing.
1238 the bombs start falling. The Ju87 had dropped to 7,000ft before beginning their steep dives. Dropping heights 800-1,500ft. Illustrious targeted by 30 Ju87 (others went other ships so splitting the fleet AA defence). This was only 13 minutes from the raid first being detected.
The attack was over in 7 minutes. That attack hit her 6 times including one of the big 1,000kg (2,200lb) bombs.
The Luftwaffe got lucky that day.
1. Illustrious' air warning radar did not prove as effective as it usually did. For an aircraft at 12,000ft the Type 279 should have been capable of detecting the attack at double the range or more. I've never seen any reason why it didn't perform so well that day. But this was still the earliest days of radar and Illustrious was the first carrier fitted with it.
2. The shadower drew the whole CAP down low (a mistake not unique to the RN and one to be repeated in the big carrier battles in the Pacific in 1942 by other navies)
3. The limited airborne CAP available had expended much of its ammo on shadowers and the TB. And given that they were scheduled for replacement around 1235-1245 would have been low on fuel.
4. There were unexplained delays in manoeuvring the fleet to allow launch the 4 extra Fulmars. Not sure if that would have made much difference though.
5. This was still the very earliest days of shipborne fighter control (less than 9 months since it had first been attempted in Ark Royal off Norway). They were still working out how to process radar information into usable plots for the FDO to direct fighters effectively and more importantly quickly. A great deal changed over the following 18 months or so.