Saving money was definitely an excuse as well but my understanding was that the old hulls had all been modded / bodged over the years and didn't therefore prese

Saving money was definitely an excuse as well but my understanding was that the old hulls had all been modded / bodged over the years and didn't therefore present a uniform integration target for new components. A bit like the failed programme to upgrade the engines in the Nimrod aircraft, where it eventually transpired that the different planes were essentially unique in terms of dimensions and design (thus requiring multiple (expensive) solutions). [Edit] Not saying that engineering difficulty was the only factor behind these cancellations, but it clearly was a significant cost driver.