Royal Navy SSNOX, SSNOY, and SSNOZ attack submarine designs


Donald McKelvy
Senior Member
14 August 2009
Reaction score
Does anyone have information, specifications, or drawings of the Royal Navy SSNOX, SSNOY, and SSNOZ attack submarine designs?

According to Rebuilding the Royal Navy: Warship Design Since 1945 by DK Brown and George Moore:

There were a large number of design studies for the next class known as SSNOX, SSNOY and SSNOZ. These were splendid designs but far too expensive, and it was agreed that the Trafalgars should be "Improved Swiftsures".

Then a Rand Organization white paper titled The United Kingdom’s Nuclear Submarine Industrial Base Volume 2 by John F. Schank et al. states that the SSNOZ was a post Trafalgar class design:

The SSNOZ (the original name for the class) was to represent a major change in capability from the Trafalgar class, which by contrast had been an evolutionary upgrade from the Swiftsure class. The SSNOZ became SSN20, whose features were to include an improved nuclear propulsion plant, an integrated sonar suite, a large increase in firepower, new combat systems, a larger pressure hull with new steel, increased stealth characteristics, and control surfaces modified for enhanced agility.

My understanding was that the SSN20 was also known as the "W-class" attack submarine.
This might be of help:,2255.0/highlight,w%20class.html

I know this is an old thread but I have been trying to track this down. Increasingly I am puzzled by the statement in Rebuilding the Royal Navy that you quoted. Rather than these designations having been for individual design studies associated with the Swiftsure class they instead appear to have been generational code names assigned as follows:

SSN-OX: Swiftsure
SSN-OY: Trafalgar
SSN-OZ: SSN20 / W Class / Astute

Eric Grove calls the Swiftsure class SSN-OX in Vanguard to Trident as does Submarine Warfare: Today and Tomorrow by John Evelyn Moore and Richard Compton-Hall who point out that a number was not used (Swiftsure became SSN07) because it was not known at what point in the build programme construction would start. The designation also makes an appearance in a number of journals from the era.

SSN-OY receives a mention in RJ Daniel's The End of an Era: The Memoirs of a Naval Constructor as being a follow on class to the Swiftsure class, he apparently argued for a simple refinement of the Swiftsure class but instead a clean sheet design was started under the designation SSN-OY: This directly contradicts DK Brown: anyone with any thoughts or info please jump in!

SSN-OZ is described as being what the Astute class was originally called in Ministry of Defence Roles and Required Technical Resources, Volume 1. That book also describes SSN20 within the context of the SSN-OZ code name. SSN-OZ also appears in at least one Government Paper as early as 1979.

In short (at least this my theory), whenever it was decided that a new class/generation of SSN was required a code name was applied, the design studies occurred under that code name and once the design was finalised and inserted into the build programme the appropriate number was added, so SSN-OX became SSN07 (Swiftsure), SSN-OY became SSN13 (Trafalgar) and SSN-OZ became SSN20 (W-class then Batch 2 Trafalgar class [itself often abbreviated to B2TC] and finally Astute). I can not find any evidence for this having started until the Swiftsure class. In terms of force planning, as far as I can make out, prior to the Nott review (Command 8288) the Naval Staff planning for SSNs had been for a total fleet of 20. The earliest coherent plan I can find any evidence for is in Hansard (1969 from Sir Ian Orr-Ewing, he is in opposition but discussing the plans during his time in government) which also states 20 SSNs with 1 to be built every 12 months (one assumes the idea is they have a lifespan of 20 years), however he goes on to state that this plan was disrupted by the Polaris programme (a 5 year hiatus is mentioned) so it was decided that this would be made up for by accelerating production to 1 every 9 months after the end of that hiatus*: obviously that never happened but the 20 target appears to have survived through to 1980/1 and was then only reduced to 17 which later seems to become 18. If one includes the cancelled 5th Resolution class boat, at its peak planning the RN was aiming for a fleet of 25 nuclear submarines.

Here's a 2011 RAND report (part of a larger study) using the Astute program as a case study:


  • a552685.pdf
    461.3 KB · Views: 121

Similar threads

Top Bottom