High Quality Content by WIKIPEDIA articles! HMS Prince Royal was a 55-gun royal ship of the English Royal Navy, built by Phineas Pett I at Woolwich and launched in 1610. She was the first ship of the line with three complete gun decks, although when first completed the upper deck carried no guns in the waist, and was stepped down aft because of the large amount of sheer (the manner in which the decks rose towards the stern and bow). In 1621 a refit saw the removal of this step-down, with all three gun decks now being continuous.