In the Cold War years of the 1950s and '60s and even into the '70s, America's nuclear arsenal -- its size, deployment, the aircraft and rockets that would deliver it and the Air Force officers and crews who oversaw it -- were front and center in the U.S. defense posture.

But there was a solid consensus among the major nations against the use of nuclear weapons for anything but self-defense. Successive presidents from Dwight D. Eisenhower on rejected any suggestions that nuclear weapons be used in South and North Vietnam.

Russia and the United States, the two great nuclear powers, maintained their arsenals as a matter of mutual deterrence, but the thawing of the Cold War led to a series of treaties placing limits on testing and the size of the arsenals.

Briefly, the peace activists' dream of a world free of nuclear weapons did not seem a total stretch. But the acquisition of nuclear weapons by India and Pakistan, which have fought four wars and often seem just minutes from a fifth; a bellicose North Korea constantly threatening their neighbors; Iran's on-again, off-again pursuit of nuclear weapons; and Islamic terrorists' determination to obtain a weapon of mass destruction mean the U.S. must maintain its arsenal to a high standard of readiness.

The Associated Press has detailed two instances this year when Air Force launch officers failed to secure blast doors intended to keep terrorists and intruders from gaining access to the missile bases' underground command posts.

For security reasons and to avoid embarrassment and awkward questions, mishaps and errors at missile bases and nuclear facilities rarely become public. One did in 2007, when six armed nuclear cruise missiles were inadvertently loaded aboard a B-52 and flown from North Dakota to Louisiana. The mistake was not discovered for 36 hours.

As in the case of the blast doors, the Air Force quickly punished the responsible officers, but that does not address the broader issue. As the AP put it, "The problems, including low morale, underscore the challenges of keeping safe such a deadly force that is constantly on alert but unlikely ever to be used."

Inescapably, however, these are problems that must be faced. Unceasing vigilance in this case is more than just a platitude; it's a vital element of our defense against an enemy that sees martyrdom as not only a tactic but a desirable goal.

McFeatters is a syndicated columnist for Scripps Howard News Service.