The review recommends modifying "a small number" of existing nuclear warheads on Trident missiles carried on USA submarines to reduce the weapons' explosive power.
U.S. President Donald Trump said he ordered Mattis to conduct the Nuclear Posture Review within days of taking office past year.
"We can not afford to let [the USA nuclear arsenal] become obsolete", Deputy Defense Secretary Patrick Shanahan told reporters at the Pentagon. Russia, China, the DPRK and Iran are among the threats to the United States.
It also casts China as a potential nuclear adversary, saying the United States arsenal is tailored to "prevent Beijing from mistakenly concluding" that it could gain advantage by using its nuclear weapons in Asia.
The new nuclear posture, in contrast, cites a more unstable geopolitical climate and the need to match capacity in Russian Federation and China to create more "flexible" capabilities - terminology many said could propel the USA into a new arms race.
Trump said the 2018 NPR addresses those challenges. "It enhances deterrence of strategic attacks against our Nation, and our allies and partners, that may not come in the form of nuclear weapons".
"The US is not arms racing, we are responding to Russian initiative here", Weaver said. "Expanding flexible US nuclear options now, to include low-yield options, is important for the preservation of credible deterrence against regional aggression", argues the Nuclear Posture Review.
The Pentagon's nuclear review is its first in eight years, and the new document closely follows its predecessor with a few exceptions. So rather than move in the direction of reducing nuclear risks by removing nuclear weapons from vulnerable sites, we will instead further cement them in place - when there is ample evidence of terrorist interest in nuclear facilities and, as is presently true in Turkey, evidence that the security of USA nuclear weapons reportedly stored there can change literally overnight.
Second, "in the longer term", the administration would develop a nuclear-armed sea-launched cruise missile - re-establishing a weapon that existed during the Cold War but was retired in 2011 by the Obama administration. The possession of such weapons coupled with a doctrine stating the right to a pre-emptive strike drastically increases the risk of a nuclear war even in "low-intensity conflicts", the Russian ministry said.
The United States now operates 14 Ohio-class ballistic missile submarines and will continue to take the steps needed to ensure those submarines remain operationally effective and survivable until replaced by the Columbia-class ballistic missile submarines, the NPR explains.
But a major United States concern is over Russian perceptions.
Speaking about the US Nuclear Posture Review released on February 2, the Russian Foreign Ministry pointed out that accusations against Moscow of aggressive behavior, interventions, breaches of arms control agreements, written in the document, have nothing to do with reality. "Clearly, the USA new nuclear strategy is a reaction to the changing global situation, which undermines the very domination of one country".
Low-yield nuclear weapons are also devastating but have a strength of less than 20 kilotons.
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