Ok. just a quick summing up: Eagle was fitted with two BS 5 Catapults 1959-64, replacing her two bow mounted hydraulic catapults. The new portside bow catapult was 151ft stroke length and could launch fully loaded Sea Vixens and Buccaneers, the new waist catapult was 199ft stroke length, and the extra power was intended to help in low/nil wind conditions often encountered in the hot and high far east. Due to the constraints of Eagle’s (and Ark’s) deck layout, it wasn’t possible to fit the longer catapult in the bow position, hence the odd sizes. Ark received two BS4 catapults (145ft stroke length) when originally fitted out (1955) and retained these until 1967,when she was refitted for Phantoms. Again she recived a 199ft BS 5 in the waist position, whilst her port forward BS 4 was rebuilt and extended to 151ft, effectively becoming a BS 5 in all but name. Additionally Ark’s catapults were fitted with a bridle catching system as the bridles used by the Phantoms were more expensive than those used by the Buccs/Vixens/Gannets. Eagle had CALE roller positioning gear fitted to her catapults (alowing aircraft to taxi on to the cat and then be lined up correctly by the gear. These were omitted/removed from Ark in 67-70. Ark also differed in having water cooled four segment Jet Blast Deflectors to cope with the heat of the Phantom’s RR Speys in full afterburner. Eagle (and Hermes, Victorious and Centaur) had non cooled steel plate JBDs, angled to deflect the jet blast upwards and overboard sideways. The other three carriers mentioned above had BS4 catapults, Centaur had two 103ft cats, as did Hermes when completed. Hermes recieved a BS4A 145ft cat in 64-66 on the portside, whilst Victorious had two 145ft cats from 1958 onwards.

All three ships had CALE gear as well. Eagle post 64 had Direct Acting Arrestor gear (DAX I), as did the others, but in 1968 she recieved a single DAX II wire for Phantom trials. Ark recieved four DAX II wires 67-70. Both Ark and Eagle’s forward cats could launch Phantoms, but if the F-4s were fully loaded for a bombing mission the waist cat was used. For the Phantom trials in 68, Eagle only used her waist cat and the JBDs were not raised, instead a thick steel plate was chained to the deck to avsorb the heat from the Spey engines. After launch, the plate which would glow white hot was cooled down with fire hoses before the next aircraft could taxi over it. All arrestor gear systems aboard ship are designed to stop the aircraft in the same distance, but the differing weights and speeds of those aircraft are dialled into the system before each recovery to adjust the tension (a phantom hits the deck a lot harder at 130 knots than a Gannet does at 90 knots.)

When the light fleets were designed in WW2, catapult launches were still optional, most takeoffs being free rolling and into wind. The catapult’s purpose was to allow more deck to be used for ranging a strike, the first half of which would be catapulted before enough deck space was available for normal rolling takeoffs. Postwar fitting steam catapults to the light fleets was something of a squeeze, and given the reduced steam plant in these ships (40,000shp/25 knots compared to the Centaurs 80,000shp/28+knots) running two cats may have been counter productive as they would have drawn more steam than could be spared without losing speed/wind over the deck.