I suspect that the Dreadnought design is too advanced to change the combat system which is a shame as the RN will be supporting two different systems for quite some time. If it’s not too late to fit the AN/BYG-1 to the Dreadnought class, there may be an additional capability available to them as the Ohio SSGN’s use the system to launch large numbers of Tomahawk missiles from the tubes previously housing ballistic missiles - it would potentially add a multi role capability to the RN CASD boats. This would obviously only be considered at a time when the strategic threat was low.
It appears that the agreement involves the upgraded AN/BYG-1 system having the British weapons integrated so that the RN can continue to use their preferred weapons. Having 3 countries using the same system will assist with keeping the development & training costs down.
The passing of the US legislation is a very significant step in this process and it appears to have a lot of bipartisan support.
https://www.news.com.au/technology/i...9edbbec8b212f7