The secondary armament of the ‘Montana’ class battleships was planned as 20 5-in (127-mm) L/54 guns in 10 turrets located as five on each side of the ships’ central superstructure ‘island’. Designed specifically for the ‘Montana’ class ships, these guns were to replace the 5-in (127-mm) L/38 guns of the secondary batteries then in widespread use on the larger ships of the US Navy. The 5-in (127-mm) L/54 turrets were similar to the 5-in (127-mm) L/38 mounts in that they were intended for the dual anti-ship and anti-aircraft roles, but differed in that they were somewhat heavier, fired heavier rounds of ammunition, and as a result caused the onset of crew fatigue sooner than the 5-in (127-mm) L/38 guns. The magazine capacity for the 5-in (127-mm) L/54 gun was 500 rounds per turret, and at an elevation of +45°the guns could engage targets nearly 26,000 yards (23775 m) distant. At an elevation of +85°, the guns could fire on air targets flying as high as 50,000 ft (15240 m).
The cancellation of the ‘Montana’ class battleships in 1943 pushed back the combat debut of the 5-in (127-mm) L/54 gun to 1945, when it was introduced on the US Navy’s ‘Midway’ class aircraft carriers, which each carried 18 such gun in single mounts. The gun proved adequate for carrier air defence, but was gradually phased out of carrier use as a result of its weight: the gun defence of carriers then passed wholly to the other ships within the carrier battle group.
For the first time since the construction of the ‘Iowa’ class, the US Navy was not building a fast battleship class solely for the purpose of escorting aircraft carriers operating in the Pacific, so the ‘Montana’ class ships were not designed for the primary task of escorting fast carrier task forces. Even so, they were schemed with a strong array of dedicated light anti-aircraft guns to protect themselves and other ships (principally the US aircraft carriers) from Japanese fighters and dive-bombers.
The 20-mm Oerlikon cannon was produced in very large numbers during World War II for aircraft and anti-aircraft use: the USA alone manufactured 124,735 such cannon. When brought into service during 1941, these cannon replaced the 0.5-in (12.7-mm) Browning M2 machine gun on a one-for-one basis. The Oerlikon cannon remained the primary light anti-aircraft weapon of the US Navy until the introduction of the 40-mm Bofors gun in 1943. The Oerlikon cannon was an air-cooled weapon based on the blowback recoil system so, unlike other automatic guns employed during World War II, the Oerlikon cannon’s barrel did not recoil, and the breechblock was never locked against the breech and is moving forward as the cannon fired. The weapon lacked a counter-recoil brake, as the force of the counter-recoil was checked by recoil from the firing of the next round.
Between December 1941 and September 1944, 32% of all Japanese aircraft downed were credited to this weapon, which reached its greatest success level in the second half of 1942, when it was credited with 48.3% of all the Japanese aircraft shot down. The revolutionary Mk 14 sight was introduced in 1943, and made these cannon still more effective. The 20-mm cannon were found to be ineffective against the Japanese kamikaze attacks used during the latter half of World War II, however, and were then phased out of service in favour of the heavier 40-mm Bofors guns.
Blogger Karl Smallwood states the following about kamikaze pilots:
“While there certainly were those who were willing to volunteer to die for emperor and country, and many more willing to die in this way simply because they felt, somewhat correctly, that they were the last line of defense to protect their families and friends at home, in truth many seem to have simply been pressured into it.”
The battery of 20-mm Oerlikon cannon which was to have been carried by the ‘Montana’ class battleships was to have been 10 and 56 single weapons of this type.
The 40-mm Bofors gun was used on almost every major warship in the US and UK fleet from 1943. Though a descendant of German, Dutch and Swedish designs, the Bofors mounts used by the US Navy during World War II had been significantly Americanised to bring the guns up to US Navy standards. This resulted in a guns system fixed to British standards with interchangeable ammunition to simplify logistics. When coupled with hydraulic drives and the Mk 51 director for improved accuracy, the 40-mm Bofors gun was devastating against shorter range air targets, and was credited with about half of all Japanese aircraft shot down between 1 October 1944 and 1 February 1945.
The battery of 40-mm Bofors gun which was to have been carried by the ‘Montana’ class battleships was to have been between 10 and 32 such weapons, the latter in eight quadruple mounts.
Aside from its firepower, a battleship’s defining characteristic is its protection. The exact design and placement of the armour constitute a complex science. A battleship was usually armoured to withstand an attack from guns of the calibre it itself carries, but the armour scheme of the ‘North Carolina’ class of 1937 was proof only against 14-in (356-mm) shells as the ships were originally to have been armed with weapons of this calibre, while the ‘South Dakota’ class of 1939 and the ‘Iowa’ class of 1040 were designed to resist only their original 2,240-lb (1016-kg) Mk V shells, not the new 2,700-lb (1225-kg) Mk 8 Armor Piercing, Capped shell actually fired by their Mk 7 guns. The ‘Montana’ class ships were the only US battleships designed to resist the Mk 8 shell, providing a ‘zone of immunity’ against the 2,700-lb (1225-kg) Mk 8 shell between 18,000 and 31,000 yards (16460 and 28345 m), and against the 2,240-lb (1016-kg) shell of the same 16-in (406-mm) calibre between 16,500 and 34,500 yards (15090 and 31545 m).
Thus the armour thickness of the ‘Montana’ class battleship included a 7.2- to 16.1-in (183- to 409-mm) belt and lower belt, 9.3-in (236-mm) armoured deck, 1.5-in (38-mm) weather deck, 0.625-in (16-mm) splinter deck, 15.25- to 18-in (387- to 457-mm) bulkheads, 18- to 21.3-in (457- to 541-mm) barbettes, 16-in (406-mm) conning tower, and turrets with 22.5-in (572-mm) faces, 12-in (305-mm) rears, 10-in (254-mm) sides and 9.15-in (232-mm) roofs.
Until the authorisation of the ‘Montana’ class, all US battleships were built within the size limits imposed by the ability to transit the Panama Canal. The main reason for this was logistical: the largest US shipyards were located on the USA’s eastern seaboard, but the nation had territorial interests in both the Atlantic and Pacific oceans, and the ability of battleships to transit the Panama Canal obviated the need for such ships to make a lengthy passage round Cape Horn. By the time of the Two Ocean Navy act, the US Navy had come to appreciate that ship designs could no longer be limited by the Panama Canal, and so approved the ‘Montana’ class knowing that the ships could not transit the canal. This shift in policy meant that the ‘Montana’ class would have been the only US battleships of the World War II period to be armoured adequately against guns of the same power as their own.
Like other major US warships of the period, the ‘Montana’ class ships were designed to use floatplanes for reconnaissance and gunnery spotting, with a secondary task of recovering downed aircrew. The type of aircraft used would have depended on when the battleships were commissioned, but in all probability the aircraft would have been either the Vought OS2U Kingfisher or Curtiss SC Seahawk. Three or four such aircraft were to have been carried for launch by two catapults and recovery by crane after alighting on the water.
The standard complement was to have been in the order of 2,355 men rising to 2,789 men as a flagship.