Raised forecastles reveal the sea a ship expects

When did unbroken decks and raised bows become normal in battleship design?

They were never universally normal; raised forecastles mainly reflect the need for seakeeping in rough operating areas such as the North Atlantic.

Cut-down decks were never a universal norm. Raised forecastles, including Dreadnought's, are associated here with rough North Atlantic conditions. Designs intended chiefly for the Mediterranean or Pacific faced different expectations for their operating waters. Iowa-class ships illustrate the further point that sea conditions can limit speed even when machinery has power available. Hull form needs to be considered alongside where the navy expects to operate.