 In 1911 , Gille went to Britain to observe the construction of the new Orion @-@ class battleships and Lion @-@ class battlecruisers . The latter ships prompted Gille to decide the French Navy ought to build battlecruisers as well , since Britain and Germany had already begun acquiring them , and they would prove useful as a fast division of the French fleet . Gille decided that his proposed ship would need a top speed of 28 to 29 kn ( 52 to 54 km / h ; 32 to 33 mph ) to retain an advantage over foreign battleships , the latest of which had estimated speeds of 22 to 23 kn ( 41 to 43 km / h ; 25 to 26 mph ) . They would also need enough armor and a main battery powerful enough to fight in the line of battle . The limitations that weight imposed on the design , however , restricted the amount of armor possible , and so the traditional French practice of armoring the entire side of the ship would be impossible . 
