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Vanguard Class SSBN Conversion To Mother Submarine
The Royal Navy is exploring future scenarios which include mother submarines. These could act as the central node on a loose network of uncrewed underwater assets. Potentially existing and planned attack submarines like the Astute Class and SSN(R) could perform the task. But there is another possibility worth exploring, at least on paper.
By 2040 the four Vanguard Class ballistic missile submarines will be replaced by the Dreadnought Class. The Vanguard Class could conceivably be modified to perform the mother submarine mission. Like the US Navy's Ohio Class SSGN conversions, these could pack a considerable land attack punch as well.
The concept was mentioned in an unclassified presentation by the Maritime Enterprise Planning Group Under Waterwater Warfare group in December 2020. That document is no longer online. It was (I believe) first reported by Naval Technology.
The Royal Navy document described a "Semi-autonomous mother submarines". The sub would launch UUVs (uncrewed underwater vehicles) to "Survey otherwise inaccessible areas".
The slide was first reported, I think, by Naval Technology.
Vanguard Conversion To Mother Submarine
I must stress that this is hypothetical, there is no suggestion that this is actually on the cards. The submarines will be long in the tooth by then, but actually comparable in age to the US Navy's Ohio Class conversions. They would also likely need reactor refueling. This has added complications in their Core-H reactor configuration, which is designed to not need refueling. But it could be done. The below outline is a mid-price option for a conversion. It would still be cheaper than building additional SSN(R)s to perform the task.
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Aside from the general modernization of internal systems which would be expected in an overhaul, the conversion would mainly affect the missile compartment. This would be extensively modified. The first six (of sixteen) missile silos would be retained. These would be reused for vertically launched missiles. From the Ohio Class conversions we know that each Trident tube can accommodate 7 Tomahawk missiles. In fact the Tomahawk launch systems from the Ohios, which would be decommissioned by then, could be acquired. Or at least copied with minimal rework.
These tubes could also carry a future precision strike missile (mentioned in the presentation). And potentially new weapons developed for the US Navy's Virginia Class submarines. These are expected to include boost-glide hypersonic missiles. Overall the mother submarine's six silos would be compatible with any payloads developed for the Virginia Classes' VPM (Virginia Payload Module). So the Royal Navy could shop 'off the shelf'.
Retaining six Trident tubes would allow for a load-out of 42 Tomahawk sized missiles. This is ten more than the Russian Navy's SEVERODVINSK-II Class SSGNS (aka Yasen-M Class). Additionally the torpedo room (more formally the Weapons Stowage Compartment, informally 'bomb shop') could still carry torpedoes and, potentially, Tomahawks etc.
Drones Mother Ship
Behind the remaining Trident missile silos is where the UUVs would be carried. Two modest-sized 'aquariums' (Ocean Interfaces) would be carried under the casing above the hull. These would allow one or more UUVs to be released or retrieved at once. They would be connected to the main hull so that UUVs could be stored and maintained aboard. These would be lifted into the aquariums.
This would allow for a massive magazine of small UUVs, roughly similar in size to current types such as the REMUS 600. Underwater gliders, valuable for their environmental intelligence (currents, salinity etc) could also be operated.
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And swarms of uncrewed air vehicles could be launched. These might be multi-rotor types which could be much larger than those deployed by torpedo tubes. The smaller Outrider type drone could also be launched.
The trunks connecting the UUV aquariums to the hull could also act as diver lock-out chambers. And as connectors to Dry Deck Shelters (DDS) attached to the casing. This would allow some larger UUVs or SDVs (Swimmer Delivery Vehicles) to be carried. Two could be carried which is double the capacity of the Astute Class. In this scenario the trunks could also be used as hyperbaric chambers for diver decompression.
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