Washington (CNN) Just as the White House is caught in a political minefield over the Russia investigation, the Pentagon is taking its toughest line yet against Russia's resurgent nuclear forces. 
 
 In its newly released Nuclear Posture Review, the Defense Department has focused much of its multibillion nuclear effort on an updated nuclear deterrence focused on Russia. 
 
 "Russia considers the United States and the North Atlantic Treaty Organization (NATO) to be the principal threats to its contemporary geopolitical ambitions," the report says. 
 
 "The Defense Intelligence Agency currently estimates Russia has a stockpile of 2,000 "non-strategic" nuclear weapons including short-range ballistic missiles, gravity bombs and depth charges that can go on medium range bomber aircraft," according to the report. 
 
 "DIA also estimates Russia has nuclear armed anti-ship, anti-submarine missiles and torpedoes. What do they need nuclear depth charges for?" one US official asked. 
 
 President Donald Trump highlighted the importance of the review's conclusions Friday in a written statement. 
 
 "Over the past decade, despite United States efforts to reduce the roles and numbers of nuclear weapons, other nuclear nations grew their stockpiles, increased the prominence of nuclear weapons in their security strategies, and -- in some cases -- pursued the development of new nuclear capabilities to threaten other nations," Trump said. 
 
 "The strategy develops capabilities aimed at making use of nuclear weapons less likely. It enhances deterrence of strategic attacks against our nation, and our allies and partners, that may not come in the form of nuclear weapons. And, importantly, it reaffirms our commitment to arms control and nuclear non-proliferation, maintains the moratorium on nuclear testing, and commits to improving efforts to prevent, detect, and respond to nuclear terrorism," he added. 
 
 The Pentagon is adamant the Nuclear Posture Review walks the line between maintaining a nuclear deterrence and encouraging controls on nuclear weapons. 
 
 "It reaffirms that the fundamental role of US nuclear policy is deterrence and continues our clear commitment to nonproliferation and arms control," said Deputy Defense Secretary Patrick Shanahan. 
 
 First mention of Russian nuclear torpedo system 
 
 The report also publicly acknowledges, for the first time, that Russia is "developing" a "new intercontinental, nuclear armed, nuclear-powered, undersea autonomous torpedo." 
 
 Known in English as the "Status-6" system, the program is described by US officials as essentially a drone-type device fired underwater that can potentially travel thousands of miles and strike US coastal targets such as military bases or cities. 
 
 Upon detonation, the device is designed to cause large zones of radioactive contamination. 
 
 Some analysts have called it a "doomsday weapon," and US Sen. Tom Cotton, R-Arkansas, has labeled the concept "destabilizing." 
 
 "The concept is a horror of the Cold War," according to Adam Mount, a senior fellow and the director of the Defense Posture Project at the Federation of American Scientists. "It is clearly inspired by overblown Russian worries that US missile defenses will make their missile forces obsolete." 
 
 "There is no indication from public information that Russia is actively developing the system, but it is alarming to see it in a Pentagon document," Mount said, adding that while the program is referenced in the Nuclear Posture Review, it is not mentioned in other government reports. 
 
 Low yield nuclear weapons 
 
 The review calls for more focus on US "low yield" nuclear weapons to try to convince Russia that the US has a credible deterrent against the potential Russian threat. The plan calls for modifying existing US warheads on submarine-launched ballistic missiles in a $50 million five-year program. 
 
 Each submarine would only carry a few of these new missiles, armed primarily with strategic longer-range missiles. 
 
 "Neither recommendation requires developing new nuclear warheads," Shanahan said. "Neither will increase the size of our nuclear stockpile. They break no treaty." 
 
 "The idea is to have one or two or just a few to address this potential Russian limited use," according to one Pentagon official. 
 
 But according to some experts, the plan translates Trump's urge to "greatly expand and strengthen" the arsenal into policy. 
 
 "The Trump administration's call for new nuclear weapons is a major shift in US policy," Mount said when asked the proposal for low-yield nuclear weapons. 
 
 "Programs for new nuclear weapons would follow our adversaries into a world where nuclear competition is commonplace. The programs would crowd out other military priorities, alarm allies, and have huge diplomatic cost -- for minimal deterrence benefit," he said. 
 
 Mount said that the review's outline for low-yield nuclear weapons "relies on the assumption that Russia would invade NATO allies, and glosses over important arguments about where and why these weapons would ever be necessary." 
 
 Low-yield ballistic missiles could be fielded within just a few years. 
 
 Longer-range missiles could come over the next decade, and the US would plan to develop and field sea-launched cruise missiles also with lower-yield warheads. 
 
 The review is calling for all of this along with an overall modernization of the nuclear force because the Pentagon requires an "investment in a credible nuclear deterrent with diverse capabilities," chief Pentagon spokesperson Dana White told reporters. 
 
 Defense Secretary James Mattis said: "What we have is a nuclear deterrent, so keep those two words always together and then look at the efforts to push forward on nonproliferation and arms control, and you have to do that when you're in a position of persuasion not of hope." ||||| Image copyright Reuters Image caption The US military is concerned that Russia is underestimating US capability 
 
 Moscow has condemned US military proposals to develop new, smaller atomic bombs mainly to deter any Russian use of nuclear weapons. 
 
 Russia's foreign minister called the move "confrontational", and expressed "deep disappointment". 
 
 The proposals stem from concerns that Russia may see current US nuclear weapons as too big to be used. 
 
 This could mean, according to the US military, that those weapons are no longer an effective deterrent. 
 
 Russia's counterblast 
 
 The Russian foreign ministry accuses the US of warmongering in its statement, issued less than 24 hours after the US proposals were published. 
 
 The latest thinking was revealed in a Pentagon policy statement known as the Nuclear Posture Review (NPR). 
 
 Russia says it will take "necessary measures" to ensure Russian security. 
 
 Image copyright EPA Image caption Russian Foreign Minister Sergei Lavrov - "disappointed" 
 
 "From first reading, the confrontational and anti-Russian character of this document leaps out at you," the statement says. 
 
 A foretaste of Mr Lavrov's anger came in a statement on Friday from the Russian senator and defence expert Frantz Klintsevich, who dubbed it "a very dangerous bet on breaking up the world strategic balance of forces" in favour of the US. 
 
 What is behind the US proposals? 
 
 They are not just about Russia. 
 
 The US military is worried about the nuclear arsenal becoming obsolete and potential threats from countries such as China, North Korea and Iran. 
 
 But a major US concern is over Russian perceptions. The document argues that smaller nuclear weapons - with a yield of less than 20 kilotons - would challenge any assumption that US weapons are too massive to serve as a credible deterrent. 
 
 Such bombs would have the same explosive power as the one dropped on the Japanese city of Nagasaki at the end of World War Two, killing more than 70,000 people. 
 
 "Our strategy will ensure Russia understands that any use of nuclear weapons, however limited, is unacceptable," the document says. 
 
 The proposed "tactical" nuclear weapons would not increase America's arsenal, which is already considerable, but would repurpose existing warheads. 
 
 Critics have accused the Trump administration of challenging the spirit of non-proliferation agreements. 
 
 What is the US doing to its nuclear weapons? 
 
 Land-based ballistic missiles, submarine-launched missiles, and air-delivered weapons - to be extensively modernised as begun under ex-President Obama 
 
 Proposed modification of some submarine-launched nuclear warheads to give a lower-yield or less powerful detonation 
 
 Return of sea-based nuclear cruise missiles 
 
 Reality Check: Where are the world's nuclear weapons? ||||| Buried In Trump's Nuclear Report: A Russian Doomsday Weapon 
 
 Enlarge this image toggle caption USAF Lookout Moutain Laboratory USAF Lookout Moutain Laboratory 
 
 The Trump administration released a report on the state of America's nuclear weaponry on Friday. The assessment, known as a Nuclear Posture Review, mainly concerns U.S. nukes and missiles. 
 
 But buried in the plan is a mention of a mysterious Russian weapon called "Status-6." On paper, at least, Status-6 appears to be a kind of doomsday device. The report refers to it as "a new intercontinental, nuclear-armed, nuclear-powered, undersea autonomous torpedo." 
 
 "The radius of total or near-total destruction is the size of a pretty large metropolitan area, actually," says Edward Geist, a Russia specialist at the Rand Corp. who has spent time looking at the weapon. "It's difficult to imagine in normal terms." 
 
 Status-6 made its first public appearance in 2015, while Russian President Vladimir Putin was visiting with his generals in the city of Sochi. 
 
 Russia state television reported on the visit. The camera shows Putin seated at a long table. Then it cuts to a shot over one of the general's shoulders. He is looking at what appears to be a drawing of a new nuclear weapon called the Oceanic Multipurpose System Status-6. 
 
 Status-6 looks like a giant torpedo about a third the length of a big Russian submarine. According to the slide, it is nuclear-powered, meaning it can roam for months and possibly even years beneath the ocean without surfacing. Its payload is a nuclear warhead "many tens of megatons in yield," Geist says. 
 
 That is thousands of times more powerful than the bombs dropped at the end of World War II and more powerful than anything currently in the U.S. and Russian arsenals. 
 
 Status-6 would launch from beneath a Russian submarine. It would shoot at a depth too deep to be intercepted and travel for thousands of miles. Upon reaching its target along the U.S. coastline, it would detonate, swallowing up whatever city happened to be nearby. 
 
 "The only possible U.S. targets are large port cities," says Mark Schneider, a senior analyst with the National Institute for Public Policy, wrote in an e-mail. "The detonation of Status-6 in any of them would essentially wipe out their population into the far suburbs." 
 
 "The detonation would cause a very large amount of radioactive fallout," adds Pavel Podvig, an arms control expert who runs a blog called Russian Strategic Nuclear Forces. Podvig believes the weapon could potentially bathe the entire Northeast Corridor in radioactive soot. 
 
 Status-6 would probably be used as a "third-strike" weapon of last resort. If Russia fell under attack from the U.S. and couldn't retaliate with its missiles, it might trigger Status-6: a doomsday machine. Or at least a doomsday-ish machine. 
 
 YouTube 
 
 Then again, the whole thing might be a fake. 
 
 "The drawing of this drone looks more like an enlarged drawing of a smaller torpedo," says Podvig. In other words, it looks as if the Russians may have just taken some torpedo clip art, blown it up to terrifying size and then broadcast it on state television. 
 
 Why? 
 
 "It's a way to get our attention," says Geist. 
 
 Geist says that the "leak" of Status-6 was deliberate. Russia worries that U.S. missile defenses might be able to shoot down its missiles in a nuclear war. By showing a plan for Status-6, Russia is warning the U.S. that if it continues to build such defensive systems, then Russia will find another way to strike, with a missile that can't be intercepted. 
 
 "My read of the whole Status-6 slide leak is that the Russians were trying to send us a message," Geist says. 
 
 Podvig agrees that the leak of Status-6 is probably just a warning shot. But the fact that it appeared in the Pentagon's newest report on nuclear weapons shows that some war planners are taking the idea seriously. 
 
 There may be some politics involved in that decision as well, says Hans Kristensen of the Federation of American Scientists. The Trump administration is pushing hard for upgrades to America's nuclear arsenal. In his State of the Union address, the president called for making the arsenal "so strong and so powerful that it will deter any acts of aggression by any other nation or anyone else." 
 
 Citing Status-6 helps to build the case that upgrades to American nukes are needed, Kristensen says. 
 
 For all the rhetoric around Status-6, Podvig and Geist both believe that the program isn't completely made-up. Geist says a long-range underwater drone without a nuclear warhead would be a useful weapon. 
 
 "You could use it for tapping our underwater communications cables," he says. "Or simpler, in a war, is just going out and like finding them and cutting them." 
 
 Status-6 could also carry conventional munitions, like cruise missiles, and launch them after hiding for months beneath the water. 
 
 Podvig has seen photos that he says indicate the Russians are working on some hardware for big underwater drones. 
 
 "My best guess is that there is there is a project to design an underwater vehicle with a purpose, unknown at this point," he says. "There is something there."
– "The detonation of Status-6 in any [large US port city] would essentially wipe out their population into the far suburbs," says a senior analyst with the National Institute for Public Policy. Status-6—a mysterious Russian nuclear weapon described in the Nuclear Posture Review released Friday by the Trump administration—is what NPR calls "a doomsday machine. Or at least a doomsday-ish machine." The report describes Status-6 as "a new intercontinental, nuclear-armed, nuclear-powered, undersea autonomous torpedo." The underwater drone could travel for years underwater and carry a nuclear payload larger than any current US or Russian weapon. While Russian state TV leaked an image of Status-6 in 2015, Friday's report is the first time the US has publicly acknowledged it, according to CNN. Russia would likely use Status-6 as a "third-strike" weapon if it's attacked by the US and unable to use its other nuclear missiles. However, it's also possible Status-6 doesn't exist. Edward Geist of the Rand Corp. says Russia may have simply enlarged a drawing of a normal torpedo "to get our attention." The Trump administration could have included it in the report to drum up support for its plan to strengthen the US nuclear arsenal. "There is no indication from public information that Russia is actively developing the system, but it is alarming to see it in a Pentagon document," says Adam Mount at the Federation of American Scientists. Elsewhere in the report, the US discusses plans to make new, smaller atomic bombs as a deterrent against Russia. The Russian foreign minister calls the plan "confrontational" and "anti-Russian," the BBC reports.