What I'm researching now, for publication in Submarine Matters tomorrow, is Why are fewer SLBMs being planned in each of the US and UK SSBN Replacements?
US 24 SLBMs down to 16 per sub.
UK 16 SLBMs down to 12 or 8 per sub.
So far variables I've taken as relevant are:
1. improvements in CEP?
2. improvements in SLBM reliability?
3. increases in numbers of penetration aids (eg. decoys)?
4. that the number of SLBM slots in the US Ohios and UK Vanguard SSBNs were always/usually excessive and/or under-used - so the reduced SLBM numbers are a rationalisation downwards.
5. are there only so many targets you need to hit to acheive an optimal deterrence?.
6. are arms limitation treaties relevant? Something I don't keep across of - as I would assume that its not only the US and Russia needing to agree these days. I also assume agreement (a political issue) would be a function of technical advantage or disadvantage.
7. are the planned reductions initial low-ball estimates, for domestic financial reasons or to keep opponents guessing?
8. A combination of variables. There will be increases in the number of MIRVs and penetrations aids per SLBM and connected with that lighter and more accurate (CEP wise) warheads/reentry vehicles.