USS Oklahoma BB-37 was the last true battleship (in the world) with triple expanders, completed in 1916. They died out in destroyers and basically in cruisers prior to WWI (the Danish hybrid coast defense ship/cruiser Niels Iuel with triple expanders wasn’t completed till the 1920’s). The last French submarines (of a number) with triple expansion steam engines for surface propulsion were also completed in 1916.
However as mentioned before, lots of minor warships (not battleship, cruiser, destroyer, but slower antisubmarine and minesweeping types) in WWII were powered by triple expansion steam engines (along with other reciprocating steam engines like the Unaflow engine). Though few warships of any type were completed with reciprocating steam engines in the interwar period, in WWII there was an industrial bottleneck in most countries to produce enough steam turbines and reduction gears for warships. Reciprocating steam as well as diesel powered lesser warships were a way around that.
Re: Kirov class, the 2 oil fired boilers naturally serve in part as a back up to the 2 nuclear reactors to supply steam to the propulsion turbines and/or the turbogenerators (43mW). The boilers are not just oil fired superheaters as was speculated in the West at one time, but standard standalone boilers, though they do have superheaters. The ships also though have a fairly large capacity of backup gas turbine powered generators, 41.5mW. For comparison the USN Nimitz class, ships about twice as powerful in total propulsion horsepower (280,000 v 140,000), all nuclear, have 4*2mW backup diesel powered generators.
Didn’t know that… why’d they do that? I was under the understanding that the New York class (*Texas *and New York) were built with triple-expansion reciprocating engines as a sort of middle-finger to the turbine companies- something like three or four previous classes of battleship had been constructed with steam turbines, and then the New Yorks were built with reciprocating engines.
What’s weirder is that the *Nevada *(BB-36, sister ship to the Oklahoma) had turbines.
The USN rapidly built 5 direct drive turbine powered coal fueled dreadnoughts, prototype North Dakota (sister Delaware had reciprocating), Florida (FL/UT) and Wyoming (WY/AR) classes before there was much time to evaluate actual fuel economy (around 30% worse for ND than DE). This was more important to the USN than other major navies because of the perceived requirement for trans-Pacific operations. Even the Japanese at that time envisioned a decisive battle with an enemy fleet relatively near Japan, as at Tsushima in 1905.
So the next class (NY/TX) was coal fired recip. In Nevada and Oklahoma the additional change was made to oil fuel, which allowed ships to carry more fuel energy for given weight and volume (higher energy per unit weight, and it fit into odd shaped spaces unlike coal) so meet a given required cruising radius with less thermal efficiency. The USN was therefore open to either engine type and accepted Fore River Shipbuilding’s proposal for a turbine ship with direct drive main turbines but geared cruising turbines for efficient low speed operation (Nevada) and New York Shipbuilding’s proposal for a reciprocating engine ship (Oklahoma). Nevada was indeed superior to Oklahoma in fuel efficiency at low speed, though burned slightly more fuel at full speed. Subsequently the PA/AZ class had a turbine arrangement broadly similar to NV’s though different in important details, then the USN went to turbo-electric drive for the rest of the pre-Washington Treaty battleships.
According to “Warships of the USSR and Russia 1945-95” by Pavlov it was because the design grew in size to require more power than two existing reactors could provide but a multi-reactor arrangement was viewed unfavorably. Although, the command ship SSV-33 had a smaller version of the same arrangement with reactors around half the size of the KN-3’s on Kirov’s, so the arrangement was preferred to bigger reactors in that case, and the nuclear carrier Ulyanovsk would have had 4 KN-3’s, so >2 reactors was accepted as a design in that case.