WASHINGTON ― There is no such thing as a “tactical” nuclear weapon, despite the introduction of two so-called tactical options in the recently released Nuclear Posture Review, U.S. Defense Secretary Jim Mattis told Congress on Tuesday.

“I don’t think there is any such thing as a ‘tactical nuclear weapon.’ Any nuclear weapon used any time is a strategic game-changer,” Mattis told members of the House Armed Services Committee.

The Nuclear Posture Review, formally released Feb. 2, called for creating a low-yield nuclear warhead for America’s sea-launched ballistic missiles, as well as the development of a new sea-launched nuclear cruise missile.

Officials rolling out the document said these weapons are needed to counter what the NPR directly refers to as Russia’s “tactical nuclear weapons.” Those weapons, which Russia is building out at a high rate, are described by the Pentagon as the backbone of Moscow’s controversial “escalate to de-escalate” strategy.

Under that concept, if fighting broke out between NATO forces and Russia, Moscow would move quickly to use a tactical nuclear weapon. The assumption would be that the U.S., armed only with large, world-ending strategic weapons, would be unable to retaliate appropriately and essentially stand down in the face of Russian aggression. Hence, the need for smaller nuclear weapons which could match Russia if need be.

While Mattis may be against the idea that using a low-yield nuclear warhead in combat does not escalate things to a strategic level, he still threw support behind the reasoning for building out the two new U.S. capabilities.

“We don’t want someone else to miscalculate and think that because they are going to use a low-yield weapon, somehow we would confront what [former Secretary of State Henry Kissinger] calls ‘surrender or suicide,’” Mattis said during the hearing. “We do not want even an inch of daylight to appear in how we look at the nuclear deterrent. It is a nuclear deterrent, and must be considered credible.”

Throwing his support behind a new nuclear cruise missile is something of an about-face for Mattis, who expressed doubts about supporting the Air Force’s new cruise missile during his January 2017 confirmation hearing.

The secretary acknowledged he came in with strong thoughts about that weapon, but said realities around the world have convinced him both it, and a new sea-based variant, are necessary for America’s safety.

“I came in wanting to challenge just about everything. I wanted it to be proven to me that we needed to spend every cent,” Mattis said, saying he was concerned the air launched cruise missile could be “destabilizing.” That is a term common among nonproliferation advocates — as well as Clinton-era Secretary of Defense William Perry — who fear an enemy nation cannot tell the difference between an incoming nuclear cruise missile and one armed with a conventional payload and would be forced to choose a nuclear response.

But after studying the issue, Mattis zeroed in on the number of nuclear cruise missiles Russia is developing, and concluded that “clearly Russia does not consider that destabilizing.”

“As I put together how I can keep us in a position where this is a nuclear deterrent, it has to have the capability to be the most persuasive deterrent in the eye of the enemy,” Mattis said. “And that was the journey I embarked on, and it was a little rough on the staff and those who came in promoting it at first, but I think they were compelling by the time they were done.”

Mattis added he believes the ICBM is a “stabilizing element” for the world, something reflected in the NPR’s full support for the Ground Based Strategic Deterrent replacement for the existing Minuteman III ICBM arsenal.