Why the submarine was named HMS Churchill

What name had originally been planned for the submarine that became HMS Churchill?

No earlier name is established. The answer argues that an order in the year of Churchill's death made the commemorative name highly likely.

HMS Churchill is described as having been ordered in October 1965, the year Churchill died. His support for British nuclear capability and submarines is given as a reason for the honour. The answer considers the choice of name highly likely once the order followed his death. It does not identify a confirmed earlier name for the submarine or class. Dreadnought, Valiant and Warspite are cited as the preceding naming pattern, followed by Churchill, Conqueror and Courageous. Courageous is said to have been intended as Superb, which is a separate naming point.