A military train that belongs to the forces responsible for Russia’s nuclear arsenal has been spotted moving toward the front lines in Ukraine, while Moscow was said to have deployed the world’s biggest submarine — capable of carrying “apocalypse” drones.

These latest maneuvers could signal an increasingly desperate Vladimir Putin’s willingness to escalate the war following a series of embarrassing defeats on the battlefield, including the loss of a key city in Donetsk and the most recent setbacks in the Kherson region.

The pro-Russian Telegram channel Rybar shared on Sunday a video showing a freight train hauling upgraded armored personnel carriers (APCs) and other sophisticated military equipment through central Russia, the Daily Mail reported.

The APCs reportedly belong to the secretive 12th Main Directorate of the Russian Ministry of Defense, which is responsible for maintaining the country’s nuclear arsenal.

Meanwhile, NATO warned its member states, including the US, that Russia’s Belgorod nuclear submarine has left its base in the Arctic Circle, the Italian newspaper La Repubblica reported.

Measuring more than 600 feet in length, the Belgorod is the largest submarine in the world. It is capable of carrying “doomsday” Poseidon nuclear torpedo drones, which, according to Russia, could trigger 1,600-foot nuclear tsunamis that would inundate coastal cities from hundreds of miles away and render them uninhabitable for decades.

The Belgorod, which only entered the Russian navy’s service in July, is regarded as “the epitome of a new concept of warfare,” and Poseidon is known as the “weapon of the apocalypse.”

“This nuclear ‘mega torpedo’ is unique in the history of the world,” American submarine expert H.I. Sutton wrote on his website Covert Shores in March. “Poseidon is a completely new category of weapon. It will reshape naval planning in both Russia and the West, leading to new requirements and new counter-weapons.”

NATO intelligence reportedly believes that the cutting-edge submarine, officially known as K-329 Belgorod, remains in the Arctic waters and may be on its way to the Kara Sea, off the coast of Russia’s Novaya Zemlya island, to conduct a series of secret tests.

Hans Christensen, director of the Nuclear Information Project at the Federation of American Scientists, noted that Poseidon torpedoes are still in the development stage and won’t be operational for at least the next several years.

The release of the nuclear convoy video and the revelations about the Belgorod submarine’s movements come after Putin made a series of veiled threats to use nuclear weapons in the war, which has been going increasingly poorly for Moscow’s battered forces.

National security adviser Jake Sullivan and Secretary of State Antony Blinken responded to Putin’s remarks by warning Russia of “catastrophic” consequences if it were to deploy its nuclear arsenal.

In a saber-rattling speech Friday at a ceremony announcing the annexation of four regions of Ukraine, Putin accused the US of creating a “precedent” for using nuclear weapons when it bombed Japan during World War II.

President Biden later issued a grave warning to Putin, saying that the US and its NATO allies were “fully prepared” to “defend every single inch for NATO territory.”

In an interview on ABC’s “This Week” on Sunday, former CIA Director David Petraeus predicted that if Putin were to deploy nuclear weapons, the US and other NATO members would destroy Russia’s forces and sink the Black Sea fleet.