Washington (CNN) The US military deployed a new submarine-launched low-yield nuclear weapon, something the Pentagon sees as critical to countering the threat posed by Russia's arsenal of smaller tactical nukes.

Several former high-ranking administration officials, however, have said the weapons increase the potential for nuclear conflict.

"The US Navy has fielded the W76-2 low-yield submarine-launched ballistic missile warhead," John Rood, the under secretary of defense for policy, said in a statement Tuesday.

The new nuclear weapon is a modification of the pre-existing W-76 warhead, which is used to arm submarine launched Trident II (D-5) missiles, so the new weapon does not add to the total number of nuclear weapons in the US stockpile.

The nuclear launch codes and nuclear options in the so-called football for the President have now been updated to reflect this weapon, a US official confirmed to CNN.

The new warheads, the first new US nuclear weapon in decades, were first produced in February of last year.

The less powerful weapon was called for in the Trump administration's 2018 Nuclear Posture Review, which warned that adversaries might believe they could use a smaller nuclear weapon against the US or its allies without fear of the US launching a nuclear retaliation due to American weapons being disproportionately more destructive.

"Expanding flexible US nuclear options now, to include low-yield options, is important for the preservation of credible deterrence against regional aggression. It will raise the nuclear threshold and help ensure that potential adversaries perceive no possible advantage in limited nuclear escalation, making nuclear employment less likely," the 2018 Nuclear Posture Review said

The plan called for modifying existing US warheads on submarine-launched ballistic missiles as part of a $50 million five-year program.

Each submarine would only carry a few of these new missiles, armed primarily with strategic longer-range missiles.

"The United States regularly consults with allies on its nuclear weapons systems, and has provided updates on its development of low-yield tridents since the 2018 Nuclear Posture Review," a NATO official told CNN.

Rood said that the low-yield weapon requirement identified in the review was intended to "address the conclusion that potential adversaries, like Russia, believe that employment of low-yield nuclear weapons will give them an advantage over the United States and its allies and partners."

He added that the new weapon "demonstrates to potential adversaries that there is no advantage to limited nuclear employment because the United States can credibly and decisively respond to any threat scenario."

Democratic House Armed Services Committee Chairman Adam Smith of Washington called the decision "misguided and dangerous".

"The deployment of this warhead does nothing to make Americans safer. Instead, this destabilizing deployment further increases the potential for miscalculation during a crisis," he added.

Russia is believed to maintain a large stockpile of "tactical" nuclear weapons, which are less powerful and destructive than those possessed by the US.

The US does have some older tactical nuclear B61 "gravity" bombs, but these are seen as much more vulnerable than a submarine-launched weapon.

The real difference is the ability to threaten "and penetrate targets deep in adversary territory that current aircraft deliverable low yield nuclear weapons cannot reach," according to Vipin Narang, an associate professor of political science at MIT.

Gen. John Hyten, the vice chairman of the Joint Chiefs of Staff, told CNN on Tuesday that submarines also offer a more rapid response option than aircraft.

"More than defendability, it's timeliness because with a submarine you can respond immediately, with a bomber you have to load the weapon and then you have to fly all the way to wherever the target is," he said.

Some have criticized the US pursuing the lower-yield weapon as some say it lowers the threshold for the use of nuclear weapons, arguing that leaders may feel less inhibited to use such weapons.

"We write to respectfully request that Congress reject the Trump administration's request for new, more usable, "low-yield" nuclear warheads for Trident missiles. There is no need for such weapons and building them would make the United States less safe. These so-called "low-yield" weapons are a gateway to nuclear catastrophe and should not be pursued," a group of former officials, including former Secretary of State George Schultz and former Secretary of Defense William Perry, wrote in 2018

One issue is that mixing low and very high yield weapons on the same boat makes it impossible for Russia or any adversary to know what is headed its way, Narang told CNN.

"They have to assume the worst, even if it is 'only one or two missiles' since the fully loaded SLBMs can carry multiple thermonuclear warheads," he said, adding that the Russians have made clear they would not wait for an incoming missile to hit before retaliating.

"So you have a system that you can never use because it buys you a strategic nuclear war. And if you can never actually use it, and the Russians know that, it cannot deter what you want it to," Narang said.

However, Hyten pushed back on criticism that low-yield weapons lower the threshold for using nuclear weapons, saying: "I don't agree with that assessment."

"The total yield of our nuclear arsenal today is smaller than it was before" the deployment of this weapon, he added.