I donâ€™t think that the costs will be as high as mentioned. A new build for just a few boats would be very expensive, but there are other options: Option 1: Extend the life of the Vanguard. This would be cheaper than new build and have the benefit of not needing any new facilities, etc etc. But, there is only so much you can do with an old boat, especially a nuclear one without the cost going way OTT. Option 2: Build a stretched Astute class. I think this idea is best as you get brand new boats, and then the Royal Navy would be operating one version of boat, which means savings on operating and training costs, equipment procurement etc. I do not think that the future deterrent needs 16 missiles (each with several warheads) in the post-Soviet world. A stretched Astute would only need half a dozen missiles, three per side mounted outside of the pressure hull. This would be more than enough of a deterrent, and would not change the shape of the stretched Astute's too much. Also, by reducing the number of missiles and warheads in total that the UK owned then we wouldn't necessary be in breach of the Nuclear Non-Proliferation Treaty. Because the Astute's will never need refuelling this will mean much reduced in-life costs. Also, in future if we did scrap all our missiles then we would have some very useful attack boats. If we retain a nuclear deterrent then it HAS to be sea based. The big problem with nuclear weapons is that in a tense political situation the temptation would be to use your missiles before you lose them, thus risking starting a war in a panic. The big advantage of submarine based missiles is that even if London is taken out etc, the deterrent is still there, available, if needed, and if not needed you haven't fired them by accident. And if you doubt the importance of that then think of this: 7,500 miles in only 30 minutes.... But the biggest advantage of going for the Astute option would be finally ending the arguments between those in attack boats and bombers!!!