 The design of what became the O 'Brien class was the result of discussions between the General Board of the United States Navy and the U.S. Navy 's Bureau of Ordnance . What resulted was a design that was an incremental development of the Aylwin class , which itself was similar to the first of the thousand tonners , the Cassin class ( which displaced about a third more than the preceding <unk> class ) . The key difference in the O 'Brien class was the increase in torpedo size , going up to 21 inches ( 533 mm ) from the preceding classes ' 18 @-@ inch ( 457 mm ) torpedoes . 
