On August 2, 2022 I wrote:
"Donor Report: UK and Australian Future SSNs Will Need VPMs
Future Australian and UK SSNs (aka SSN(R)) will need at least two vertical firing Virginia Payload Modules (VPMs). This is because the hypersonic missiles being developed will be of larger diameter and likely longer/taller than the UK RN's 533mm torpedo tube fired 520mm Tomahawks. VPMs will very likely be in US Virginia Block Vs and maybe VIs and VIIs.
Instead the most likely hypersonic missile the USN is likely to adopt and adapt is the US Army's Long-Range Hypersonic Weapon (LRHW) reportedly 880mm diameter (right sidebar) with a range around 1,725 miles at Mach 5+. The USN intends to procure a ship/submarine-launched variant of the missile as part of the USN's Intermediate-Range Conventional Prompt Strike (IRCPS) program.
Peer-enemies are increasingly capable of firing supersonic or hypersonic anti-submarine, anti-ship and land attack missiles over distances greater than a subsonic Tomahawk's. This is a technology driver for hypersonic missiles in the future US, UK and eventually Australian SSN corps.
The RN is likely to adopt the hypersonic missile the USN adopts out of interoperability, commonality, lower development and unit cost considerations. This is in the tradition of the RN adopting US Harpoon, Tomahawk, Polaris and Trident II missiles.
Instead of 7 x Tomahawks in a VPM only 3 x 880mm Hypersonic Missiles might fit. There is also a possibility that in the more distant future a longer/taller hypersonic missiles, range 3,000+ miles, might need to fit into VPMs.
The UK Astute's current 6 x 533mm torpedo tube arrangement could possibly be upgraded to 650mm tubes (like US Seawolfs) but horizontal tubes of 880+mm with increasing lengths would be out the question.
There would not be a larger horizontal tube retrofitting option for the RN either, as this would mean weakening the hull (with major cutting and widening of holes) and major torpedo room rearrangements, including substantial lengthening.
VPMs also allow faster dedicated ripple firing in the face of increasing rapid detection by the enemy who may fire new generation torpedo carrying ASROC missiles in response.
Also perhaps 2 of a UK SSNs 6 torpedo tubes may need to carry torpedoes leaving just 4 tubes for missiles, with the need for follow-on reloading.
VPMs can also be adapted to handle Diver/Special Forces stores, rapid diver access, diver delivery vehicles and also large UUVs better than horizontal arrangements. Whether buying US Virginia Mark Vs or UK SSN(R)s Australian SSN selectors would do well to include VPMs."
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On Jan 7, 2023 I wrote "US Nuclear Weapon Sharing Under AUKUS? Addition." at https://gentleseas.blogspot.com/2023/01/us-nuclear-weapon-sharing-under-aukus.html
which included:
"Regarding SSN platforms 4 or perhaps 12 (3 per Virginia Payload Tube (VPT)) vertically launched hypersonic missiles, called Long-Range Hypersonic Weapons (LRHWs), could be carried on each SSN. LRHWs, with a range of 3,000km, may be deployed by the US Army as early as 2023 and on USN Virginia SSNs by the late 2020s. UK SSN(R)s, maybe available in the 2040s, might also be armed with 4 VPTs (hence 12 hypersonic missiles)."