freeboard led to frequent water ingestion over the bow and in the torpedo compartments and lower aft casemates. The lightly built hulls leaked, so that sustained high-speed steaming contaminated the oil tanks with sea water. A serious flaw in these ships' subdivision was the complete lack of watertight bulkheads anywhere above the main deck or aft on the main deck. These drawbacks notwithstanding, the US Navy took some pride in the Omaha class. They featured improved compartmentalization; propulsion machinery was laid out on the unit system, with alternating groups of boiler rooms and engine rooms, to prevent immobilization by a single torpedo hit. Magazines were the first to be placed on centerline, below the waterline. These were also the first U.S. Navy cruisers designed after the switch from coal to oil-fired boilers. Originally designed to serve as scouts, they served throughout the interwar period as leaders of fleet flotillas, helping them resist enemy destroyer attack. Tactical scouting became the province of cruiser aircraft, and the distant scouting role was taken over by the new heavy cruisers spawned by the Washington Naval Treaty. Thus, the Omaha class never performed their designed function. They were relegated to the fleet-screening role, where their high speed and great volume of fire were most appreciated. Armament changes During their careers the Omahas went through several armament changes. Some of these changes were to save weight, while others were to increase their AA armament. On 8 September 1926, the Chief of Naval Operations, Admiral Edward W. Eberle, along with the Commanders in Chief of the United States Fleet and Battle Fleet, and their subordinate commanding officers, the Secretary of the Navy, Curtis D. Wilbur, ordered that all mines and the tracks for laying the mines be removed from all of the Omaha-class cruisers, as the working conditions had been found to be very "wet". In 1933–1934, their 3-inch AA guns were increased from two to eight, all mounted in the ship's waist. The lower torpedo tube mounts, which had also proved to be very wet, were removed and the openings plated over before the start of World War II. After 1939, the lower aft 6-inch guns were removed from most of the Omahas and the casemates plated over for the same reason as the lower torpedo mounts. The ships' AA armament was first augmented by three quadruple /75 gun mounts by early 1942, however, these did