LA VISTA, Neb. – Deterrence is not limited to nuclear weapons, but conventional arms and ballistic missile defense cannot substitute for the United States nuclear triad, a senior Defense Department official said here on Thursday.

“Most of you have heard me say too many times that deterrence is not limited solely to nuclear weapons, non-nuclear strategic capabilities, be that ballistic missile defenses or investments in capabilities for conventional strike systems,” Elaine Bunn, deputy assistant secretary of defense for nuclear and missile defense policy, said during a panel discussion at the 2015 U.S. Strategic Command (STRATCOM) deterrence symposium. “All those play a very important role in deterrence. However, they are not substitutes for nuclear weapons.”

A trail from a recent Minuteman III test launch from Vandenberg AFB, Calif. Photo: Air Force.
A trail from a recent Minuteman III test launch from Vandenberg AFB, Calif. Photo: Air Force.

While Bunn said it is “unfortunate” that the U.S. faces the challenge of modernizing its full nuclear portfolio amid a tight budget environment, she cited the necessity of nuclear arms to assure allies and deter potential adversaries.

“Nuclear weapons are uniquely suited to a limited role, but a critical role,” she said. “There’s no single universal force that best fulfills that goal…There’s not any special equation that tells us definitively  what we need. Instead, it depends on qualitative judgments on issues. It depends on our judgment on the international security environment and the trends that will shape what it looks like in the future. It depends on the security concerns of our allies.”

Several U.S. nuclear capabilities are expected to age out in the next 15 years, including the Ohio-class submarine, the Minuteman III ICBM and the Air-Launched Cruise Missile (ALCM). Officials have described the expected cost of nuclear modernization as a looming “bow wave.”