In 1959, the U.S. Air Force deployed its first intercontinental ballistic missile at Vandenberg Air Force Base in California. A year later, the Navy deployed its first submarine-launched ballistic missile aboard the submarine George Washington. These systems, together with the Air Force’s nuclear-capable bomber force, formed the United States’ nuclear deterrence capability, which came to be known as the “triad.”

The triad has been the foundation of U.S. national security policy for over 60 years, providing stability to America’s global military operations and diplomacy efforts. The triad — and the security umbrella it extends to our allies and partners — has fostered decades of peace and prosperity. Nuclear deterrence has successfully prevented crises from escalating to conflicts and promoted cooperation and diplomacy in resolving disputes.

Today, nuclear deterrence is more important than ever, which is why we must prioritize efforts to modernize the triad.

Throughout the Cold War and into the 21st century, military and political leaders have worked together to maintain a credible, safe and reliable nuclear deterrence capability. As technologies and threats evolve, so has the triad. Over the years, each leg has been modernized several times.

Currently, the Air Force is developing the B-21 long-range strike bomber, which will enter service later this decade, and the Navy is replacing its fleet of ballistic missile submarines with the Columbia class, scheduled to begin patrols in 2031.

A replacement is also needed for the Minuteman ICBM system, which first entered service in 1962 and has been upgraded and extended 40 years beyond its original service life. In 2010, after affirming the importance of maintaining a land-based leg, the Obama administration initiated the Ground Based Strategic Deterrent program, a modern ICBM system that will improve reliability, lower operational costs, and respond to current and future threats.

The Air Force will soon begin work on GBSD, which will enter service in 2029. Over 10 years of planning have led to this goal, with the program’s necessity validated by two presidential administrations, six congresses and six secretaries of defense.

ICBMs are an integral part of the triad, providing complementary capabilities to the sea-based and bomber legs that enhance our overall deterrence posture. For example, land-based missiles are the most robust and stabilizing leg of the triad. Consisting of 400 active, hardened missile launch facilities on sovereign U.S. soil and dispersed over 30,000 square miles, ICBMs pose a nearly insurmountable obstacle to those who wish us harm. They prevent any rational adversary from credibly threatening or confidently planning a strike.

Failing to adequately maintain the land-based leg of the triad by fully funding the GBSD would threaten strategic stability and make remaining U.S. nuclear forces more vulnerable. America’s ICBM force is both affordable and cost-effective — it features the lowest annual sustainment and recapitalization costs compared to the other two legs. It is vital the nation maintain its nuclear force posture, which has acted as a stabilizing element of global security for decades.

Modernizing the triad is no small undertaking, and our current modernization efforts are the result of decades of careful planning and bipartisan support. Stewardship is handed down from one set of leaders to the next, and in this critical moment of transition it is imperative our current leaders keep these modernization programs on track. We strongly recommend that members of Congress support moving ahead with the GBSD program so it can join the other legs in providing effective deterrence for decades to come.

The contributors to this commentary are: Former U.S. Air Force Secretaries Sheila Widnall, Whitten Peters, James Roche, Michael Wynne, Michael Donley and Deborah Lee James, as well as former U.S. Air Force Chiefs of Staff Gen. Larry Welch, Gen. Merrill McPeak, Gen. Ronald Fogleman, Gen. Michael Ryan, Gen. John Jumper and Gen. T. Michael Moseley.