When ironclad frigates performed the battleship role

Did the Royal Navy briefly have no battleships during the transition from sail to steam and steel?

No; ironclad frigates such as Warrior performed the battleship function before the terminology settled.

Ships such as HMS Warrior were formally described as ironclad frigates even though they fulfilled the role later associated with battleships. The transition from the sailing rating system through ironclad frigates to ships explicitly called battleships makes a name-based list look emptier than the fleet actually was.