February 1945. Propulsion The propulsion plant of the Montanas would have consisted of eight Babcock & Wilcox two-drum boilers with a steam pressure of and a steam temperature of feeding four geared steam turbines, each driving one shaft with ; this would result in a total propulsive power of , which gave a design speed of 28 knots at 70,500 tons displacement. While less powerful than the powerplant used by the Iowas, the Montanas plant enabled the machinery spaces to be considerably more subdivided, with extensive longitudinal and traverse subdivisions of the boiler and engine rooms. The machinery arrangement was reminiscent of that of the , with the boiler rooms flanking the two central turbine rooms for the inboard shafts, while the turbine rooms for the wing shafts were placed at the after end of the machinery spaces. Montanas machinery arrangement combined with increased power would eventually be used on the . The Montanas were designed to carry of fuel oil and had a nominal range of at . Two semi-balanced rudders were placed behind the two inboard screws. The inboard shafts were housed in skegs, which, while increasing hydrodynamic drag, substantially strengthened the stern structure. To meet the high electrical loads anticipated for the ships, the design was to have ten 1,250 kW ship service turbogenerators (SSTG), providing a total of 12,500 kW of non-emergency electrical power at 450 volts alternating current. The ships were also to be equipped with two 500 kW emergency diesel generators. Armor Aside from its firepower, a battleship's defining feature is its armor. The exact design and placement of the armor, inextricably linked with the ship's stability and performance, is a complex science honed over decades. A battleship is usually armored to withstand an attack from guns the size of its own, but the armor scheme of the preceding North Carolina class was only proof against shells (which they had originally been intended to carry), while the South Dakota and Iowa classes were designed only to resist their original complement of Mk. 5 shells, not the new "super-heavy" Mk. 8 armor-piercing shells they actually used. The Montanas were the only US battleships designed to resist the Mk. 8. They were designed to give a zone of immunity against fire from 16-inch/45-caliber firing 2,700 lb shell, between and 16-inch/45-caliber firing 2,240 lb shell, between away. As designed, the Montanas used the "all or nothing" armor