What killed Ikara in the end was the proliferation of small choppers onboard all ships. You could do what Ikara did, plus a whole lot more with a chopper. However, that was really until the mid-1970s. Before then, small ships need an ASW missile launcher, otherwise they had no means to prosecute a contact over the horizon. The RAN's Daring class showed how you could put an Ikara launcher on a small platform. It was quite an engineering achievement.
Ikara wasn't on the Darings, it was on the Rivers and the Perths.
I'd suggest that a helo is not a perfect substitue for an ASW missile, and the fact that navies who can afford both continue to do so (principly the USN and the JMSDF) bears that out.
1. The very versatility that makes a helo so attractive may mean that it's off doing some other mission, with the wrong weapons in the wrong place, when you urgently need it to attack a submarine. The fact that an ASW missile can't do anything else means it's always available for it's primary mission.
2. The helo's reaction time is very variable, even if it is available. If it's on top of the contact then it's very quick indeed, but if it's 10 miles away, or it's just run out of fuel and/or weapons, or it's packed up in the hangar at 2.00am, then it can't compete with an ASW missile.
3. The helo's availability is poorer than an ASW missile. It needs regular maintenance, it breaks down, and it can crash or get shot down. If you fire an Ikara in atrocious weather and it crashes or fails, then you can fire another one. If you launch your one-and-only helo is the same conditions (assuming you can even do that) and it crashes, then you're down to your triple lightweight TTs. Good luck with that...
Don't get me wrong, helos are a good ASW weapon, but they're a
different ASW weapon from a missile: helo and missile are actually very complimentary. I think the "triumph" of helos over ASWMs has more to do with priorities in the face of shrinking budgets. The helo is genuinely more versatile and can do useful (and photogenic
) things in peacetime too.
The advantage the RAN's launcher had over the RN's was that it used electric motors, whereas the RN's used hydraulics. The electrics were much quieter in operation, whereas the hydraulics were as noisy as all hell (and slower in operation). The Submarines apparently could hear the hydraulic pumps start up and the launcher train whereas they couldn't hear the electrical ones.
The "reason" for the the different RN launcher and magazine arrangements was because they thought they were going to get a nuclear depth bomb payload for it, which never actually materialised. Their lordships didn't like the idea of a nuke fired "in roughly the right direction" from the simple Aussie launcher, so they demanded the pointlessly precise Vickers one, that added no practical benefit and made more noise. An idiotic decision.
The RN magazine setup makes a bit more sense for carrying nukes. The Aussie one was a horizontal "hanger" on the same level as the launcher and assembly room, with little or no practical access to the missiles once they were inside. To carry nukes, the RN insisted that the magazine be below the waterline and that a magazine crew have access to the weapons in it in order to swap a torpedo for a nuke should the need arise. The arrangement on Leanders (and I presume on
Bristol) had the missiles stowed vertically on shockproof pedestals in two rows in a deep magazine with access in between them. They were picked up by an overhead grab running on a rail and transfered to a hoist which took them up to the assembly room.
Putting missiles on a launcher is simpler than adding multiple launchers of different types on a ship hull, with all the associated magazines and handling rooms, which is why I'd suggest adapting the Ikara launcher to fire the SAM of choice. All the system then has to do is gather the missile and guide it and the magazine and handling paths are eased.
The Ikara missile is such an odd shape, and the launcher operates in such an odd way, that I can't imagine what other missile could use it without major modifications to either or both. The Ikara launcher wasn't particularly reliable either (maintenance difficulties were cited as one reason for retiring it) and sometimes actually damaged rounds, leading to a particularly tasty safeing job for the armourers. It must be significant that all three attempts to update or replace Ikara have started frim the position of making it containerised.