I think CW's self-confidence drove him further ahead than if he just gave up post-Anne. However, I wonder if he had help from Adm Croft, whatever his position was in the Navy 8 years ago?

As others have mentioned elsewhere, apparently it's not easy to get a ship even if one was made a commander, as there were many commanders and fewer ships. So for CW to get a ship, he must've had some sort of connection, at least to to get his foot in the door. Once in, he could then wield his self-confidence and keep the ship.