 All these vessels had a distinctive "turtleback" forecastle that was intended to clear water from the bow, but actually tended to dig the bow in to anything of a sea, resulting in a very wet conning position.They were better constructed than their A-class forebears (the "26 knotter" and "27 knotter" groups), but still were poor seaboats unable to reach top speed in anything but perfect conditions.They generally displaced 355 to 370 tons and had a length of .