Why battleship conning towers have different shapes

Why are some battleship conning towers circular while others are oval across or along the ship?

The shape reflects design priorities, hull balance and the space needed for command functions and personnel.

Conning-tower shape depends partly on what designers expect the position to contain and do. More command functions and personnel require more internal space. Designers must fit that space into the ship and its balance. A circle can be treated as an ideal shape, while an oval can provide a practical fit for a particular requirement.