The primary problem with the RN and HMGovernment is that you spend forever designing a ship, instead of making a design that you can build for 4-6 hulls
right now and while those are building you work an improved design to build for 4-6 ships that will start building as soon as the ways are clear from the last class, rinse and repeat.
The current process means that you don't keep the shipyards busy (and all the economic activity related to the workers flowing), instead you leave the yards idle for way too long. So the yards lay off their workforce, and when the next ships come to be built the newly hired workers don't have a clue. Workers not having a clue means that the ships have build quality issues. All those new workers needing to have a security background check done on them also slows down the start of construction.
Compare the UK to Japan. In 1997, the UK's GDP was $1.5T, while Japan's GDP was $4.5T. However, Japan only spends 1% of GDP on their military
at most*, while the UK could realistically spend 3% and call it a spending reduction from the 5.6% they had been spending. So the UK could build ships like Japan does, constantly having one ship of each type under construction and alternating which yards are building. There's also the possibilities of buying production rights to a US design, say the FFG-7s or even Burkes, making a couple modifications to them and running with those. Japan did that with their Kongo class DDGs, and then further iterated on that design for the following Atago and Maya classes. The Kongos were built starting in 1990, first ship commissioned in 1993, even, so the Japanese pretty quickly decided that they wanted an Aegis ship and just bought the current production US plans.
IIRC, Japan has been slowly growing their navy, but since I'm having a hard time finding an online reference for what they had in 1997, I'll go with their current fleet.
- 22x (diesel-electric) submarines.
- 4x "Helicopter Destroyers", "Through-deck cruisers", or baby aircraft carriers (2 are 19k tons, 2 are 27k).
- 3x LSTs; the stern has a huge flight deck and should really be classed as LPDs.
- 8x DDGs, and 28x DDs.
- 10x frigates.
- 22x minesweepers.
- 6x patrol boats.
Yes, the baby carriers are a recent addition to the fleet, but they were still built under the unofficial 1% spending cap.
In comparison, the RN currently has:
- 4 SSBNs,
- 6 SSNs,
- 2x QE-class carriers,
- 3x LPDs,
- 6x DDGs,
- 11x Frigates,
- 8x OPVs,
- 9x minesweepers, and
- 18x patrol boats that I don't even think have a weapon onboard.
* Japan's spending as a % of GDP has finally increased, but that was in the 2010s.
On the original question from 1997 the choices to shape the RN are mostly limited to the new carrier, T45 and subs. From a policy POV the sub program as is has little potential for worthwhile chwnge unless you were to build the Astute class as a multi-role SSN/SSBN. Maybe a class of 12 with Astute like capabilities but with eight reconfigurable Trident capable vertical tubes. Could sail as a nuclear deterrent boat or land attack (TLAM in the vertical tubes) or SOF (SBS in the tubes). Carriers are always about the aircraft and JSF requires something like the QEC. Is there an alternative aircraft? Not really. Maybe you could go all helo. Build a Sea Apache to provide anti ship/boat/insurgent and use SAMs for air defence. SM6 with a Merlin/AESA AEW would be quite capable for fleet defence. If you go this way then something like a 21st century through deck cruiser could be built in place of T45 and CVF. Eight of these each with two T23 consorts and an air group of 12 Sea Apaches, 6 Merlin ASW and 6 Merlin AEW would be quite impressive. Fitting the CAH or a conventional T45 with AEGIS is a much better solution than PAAMS. Anyway the multi role sub and multi role cruiser/carrier are radical solutions so hard to sell and result in an end to naval carrier strike. But they retain and spread capabilith making for a lower cost and more resiliant (to political threats) force.
Your suggestion of an SSN/SSBN interchangeable type design was looked at by the Royal Navy when they started to to at the adoption of Polaris. This type of vessel was ruled out as an SSN is there to hunt and destroy enemy vessels whereas the SSBN‘s job is to ‘disappear’ in the vastness of the oceans.
regrettably, the two rows do not lend themselves to a single unit type design.
Agree with Pirate Pete, an SSBN's job is to be at sea 24/7, with no-one knowing where it is. The US Ohio class manages to be at sea for 3/4 of the year by using two crews and a lot of planned replacement of parts before their expected failure actually happens.
The deterrence mission just flat requires permanently assigned units to it.
The reason the USN turned old SSBNs into special ops and Tomahawk boats is that they had SALT and START treaty obligations on the number of deployed launchers they could have, but the Ohio boats still had 20 years of hull life left in them. All of the strategic missile control systems had to be ripped out of the hulls, and an amendment to the treaties negotiated in the definition of what defined a strategic missile tube. The treaties originally defined the strategic tubes by diameter, the US requested an amendment for either diameter or depth. A Polaris missile is 33 feet long, but a Tomahawk is only about 25 feet long. Any missile tube over whatever the magic diameter was, that was less than something like 30 feet deep, was not considered a strategic tube. Completely different situation.
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That said, there is absolutely no excuse for the RN taking an 11-year break between completing the Vanguard class and starting production on the Astutes. Having trouble with the shore-side tech demonstrators? Do another run of Trafalgar class boats to keep the yards working while you fix the Astute design! It's vastly cheaper than letting the shipyard idle. Even the US had to do this when the Seawolf class was canceled after two ships with nothing to build for 3 years before the Virginia class started construction. Bill Clinton was explicit that the 3rd Seawolf was halfway a jobs program to keep the yard busy! Admittedly, USS Parche was getting close to retirement and did need a replacement, so taking one of the quietest ships in the world and installing a plug for spooky shenanigans was a good plan. Saved sawing a 688 in half and installing a plug.