ASW is a carrier role. The carrier will provide helicopters for 24/7 dipping, working with frigates with towed array sonar. The predecessors of the
Queen Elizabeth class were the
Invincibles, which started life on the drawing board as through deck cruisers intended to embark up to ten ASW Sea Kings. The United Sates used to operate dedicated ASW carriers as well as attack ones, until the two roles were combined in the same ship and air wing in the seventies.
Back in the eighties, with less capable sonars aboard both ships and aircraft:
Our bread & butter was the so-called "Ripple 3"; 3 aircraft airborne all the time (2 on task, with 1 in transit to / from the scene of action) 100+ miles away from the carrier / convoy, sometimes for weeks at a time. I joined 820 NAS / Ark in late-86, and the first thing we did was a major NATO exercise escorting a convoy from Norfolk VA to Harstad in Northern Norway - we had 3 aircraft on task for over 3 weeks, non-stop. I shudder to think how many sonobuoys we "spat" in a 3000+ mile line across the Atlantic. [100+ miles away, by the way, because by then the Soviets had developed long-range missiles that they could fire from e.g. a Charlie class SSN, thus attacking the convoy without having to get all that close - [b]targeting info coming from Russian aircraft, which was one of the original reasons for procuring the Sea Harrier]. It was tiring, but possible to keep it up almost indefinitely - we had 14 crews, and 9 aircraft, so even if you had, say, 4 cabs broken at any time (not uncommon!), there were enough to keep the Ripple going. You got into a rhythm: wake up; eat; brief an hour before take off; fly for 4 hours; debrief [& file your records if you'd come across any real Soviet boats]; go to bed... 6 hours later repeat... and repeat... and repeat...
But if it's an airborne frigate, why do you need 2 on task? Because it gives you much more flexibility; for instance, one of the Soviet tactics was so-called "sprint & drift" - if it thought it had been detected (and if you flew too low they would hear you), the SSN would wind up to 30kts and shoot off 50 miles or so, and then suddenly go completely silent; slow right down and use natural salinity / temperature layers in the water to interfere with sonar. If you only had one aircraft, he would have to be incredibly unlucky for you to keep up with that - effectively his boat simply disappeared. But with two, provided you were worked up and in good practice, one of you could track the boat while it was fast (& noisy) and direct the other to fly ahead... and then swap. If they didn't know you were there, then over time it was possible to get a really accurate picture of where the boat was (all passively) - so one of you would run the plot, and use the other cab as the weapon carrier. Or, if in doubt, direct the other cab into a hover ahead of the target... ping... contact... weapon in the water within seconds before he has time to react.
At its worst, this was soul-crushingly boring. Stooging around for 4 hours at 6000'+ (nosebleed territory for helicopters) at maximum endurance speed (c.65 kts), in the dark so on instruments, spitting sonobuoys and finding... diddly squat. But when you were in contact - which was often with the real thing (e.g. on that 3 weeks crossing the Atlantic, we detected and tracked around 10 Russian SSNs [probably not 10 separate hulls, but 4 different types, so deffo not the same bloke 10 times!], since they were just as interested in watching us practice as vice versa) - it was 3-dimensional chess; it could be really exciting. Sometimes the SSN drivers would get bored, or decide to test their own tactics (we never knew), so they'd give up trying to be sneaky-beaky and stay silent, and instead try shaking us off with speed, big sudden changes in course, decoys etc. Tracking a fast nuke, in daylight, with 2 aircraft using both passive and active techniques - very, very demanding, but enormous fun.
From
here.
Things have changed since then - active dipping sonar is the main ASW sensor. NATO has conducted major ASW exercises with a carrier at the centre of the task group in
2014 and
2016. NATO still depends on moving forces by sea, and having amphibious capabilities.