The turrets of the Renown class were known as A, B & Y, The courageous class had A & Y, The Lion class and Tiger had A, B, Q & X, The 12in battlecruisers had A, P, Q & X. All the above ships had a single turret aft on a deck known as the poop deck or quarterdeck, I believe the different names for the same area of deck depended on how the ship was designed/arranged. Why were the single aft-most turrets given different letters? Is it because the turrets were possibly on different deck levels, or does the name of the deck [poop or quarterdeck] affect the letter applied? E.g. turrets on a poop deck are termed X while a turret on a quarterdeck is termed Y?