Shipbucket

Awesome guys, thanks for all the help. I've done a bit more research on the submarines and I'm thinking I might go with small nuclear boats - something between the Rubis and Trafalgar in size, where the manning requirement doesn't seem too unreasonable (though I'm still not sure if this will potentially reduce the number of boats I could have compared to conventional subs? - most countries seem to only have 6-7 per class...). For the Recherche Navy I'm thinking the tactical flexibility of nuclear subs outweighs any extra noise they may make compared to an SSK.

For the first carrier I think I'll go with Timothy's suggestion and go for steam turbines with diesel backups, should be a fairly simple arrangement even if acceleration suffers.

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The main advantage that SSNs have over SSKs is the ability to sustain high speed transits for extended periods - It's going to be able to run at least at 20 knots all the way around the world if it has to. While the SSK might be less noisey under some situtations (when running on batteries for example) it's not going to be less noisey while transiting.
That suggestion was only for the 1980s design as after that you start getting into improved gas turbines that offer power compactness that starts to outweight the disadvantages vs. Steam.

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𝐌𝐀𝐓𝐇𝐍𝐄𝐓- 𝑻𝒐 𝑪𝒐𝒈𝒊𝒕𝒂𝒕𝒆 𝒂𝒏𝒅 𝒕𝒐 𝑺𝒐𝒍𝒗𝒆

Yeah that's the main reason I'm leaning towards SSNs, as good as an SSK might be you can't really rush them anywhere...
I'm figuring electromagnetic catapults would be feasible in the 2015-2020 time frame also?

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Allow me to point out that making smaller nuke boats is an excersize in futility: They simply aren't large enough to have significant noise-cancelling measures. The French Rubis class is supposedly horribly noisy.
Also, designing and maintaining nuke infrastructure for a single nation is going to be expensive.

Since Recherche is still a Commonwealth nation, bite the bullet, and see if you can find a way to go Trafalgar.

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Would you please not eat my gun...

By small I was thinking along the lines of between a Swiftsure and Trafalgar as opposed to a Los Angeles for example, with an in service date of around 2010 - would that still pose the same problems you stated?

As for cost it will be expensive - in the real world probably unreasonably so - but I figure I can stretch the truth every now and then. My main reason for not just going for a Trafalgar (other than time frame) is that then I won't get to draw the submarine myself, and in this AU there is a lot of technical cooperation with a slightly more financially healthy UK so I'd imagine that would help reduce certain costs.

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If you're going for UK cooperation, you're going to end up with some kind of Astute. Which BEGAN as a design for a Trafalgar with an updated reactor core. Designing a nuke sub is a very dedicated process, and even the Brits had lost enough expertise that they needed US help to get the Astute program going. Having Recherche in the program might help enough that the first Astute boats will be delivered earlier, and without US help. But they're not going to be designing two completely different boats.

Realistically you're not going to get a boat smaller than a Trafalgar, and if you're going for the Never-refuel PWR-2 reactor (this lessens the industrial base you need) you're basically looking at a boat the size of the Astute. The PWR-2 is not small, and it drives the size of the pressure hull.

Of coure you can decide you don't need the huge sail with the spec ops lockers, which means the hump goes as well, you gain some top speed, and you can change the rudders to an X configuration if you think you need to bottom out/operate more in brown water, but if you're working with the UK, you'll end up with an Astute-lite.

Which admittedly is a very very nice thing to have.

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Would you please not eat my gun...

Like you said, you can't really rush an SSK anywhere, however that brings up the question do you need to?
SSKs are undeniably cheaper to build and since they tend to be smaller and have significantly smaller crews they're also cheaper to operate. That means you can have more boats which should help tremendously with availability. As long as they don't have to travel a long way under water to get there their time on station isn't all that much shorter than a nuke boat.

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“Close” only counts with horseshoes, hand grenades, and tactical nuclear weapons.
That which does not kill me has made a grave tactical error

Worklist

Source Materiel is always welcome.

What Thiel says is true.

You could allways piggyback onto the Australian Collins program, AFTER they've learned from some of their more egrarious mistakes. Or buy French.

Or buy early and support the Dutch before they lost their submarine building capabilities. The Walrus class was an extremely capable boat when first launched, an AIP follow-up would be right up your alley.

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Would you please not eat my gun...

SSKs it is then. The logical part of me was telling me that SSKs were better in most of the things I was looking for (expense, crew size, hull numbers etc.) but the other part of me loved the idea of a higher transit speed
Thanks for the help and insights, I know very little about sub design so this has all been very helpful

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In terms of a SSK, considering the Commonwealth's apparent close relationship with the UK in terms of the Cascade and the Esperance class, could their be any interest in working with the UK on the Upholder class? I know that they have had less than an ideal service life but say if the UK had a confirmed export customer of 8-12 boats in the early 90's things would be different for the class? I know in OTL they have had less than an ideal live but with this TL it could be different

For another option, I say the modern U214-U216 family wold be an option. Just my thoughts anyway.

BTW Rowdy brilliant thread that I've enjoyed.