Anons were asking in last bread about subs that have the capability of launching the type II D5 Trident.
It may help to understand that the Trafalgar Class UK subs aren't submarines that can house D5 Type IIs. That would not be adequate.
The Trafalgar Class Trident capable submarine is a set of of Trident multi re-entry vehicle intercontinental ballistic missiles with a submarine built around it.
These multi stage rockets require their document vehicle to be designed for it. They cannot just be stuck on the outside of another sub and light a match under it.