RUTHFULLY YOURS

It was simply called the “Dayton Exercise” and for obvious reasons it was kept secret for decades. It was also one of the clearest examples of the trouble the United States encounters when it decides to precipitously draw back its military in a troubled world.

At the end of World War II, the U.S. had the most modern and best-equipped military on earth. No one else came close. It had taken the entire war to build it, and at great sacrifice.

U.S. troops fought at a distinct disadvantage until 1944 because of an earlier self-imposed disarmament. But when the atomic bombs fell on Hiroshima and Nagasaki, forcing the Japanese surrender and preventing a land invasion of the Japanese islands, the U.S. abruptly demobilized again. It had done the same thing 27 years earlier, after World War I.

In the Army Air Forces alone (there was no independent Air Force until 1947), the number of men dropped to just over 300,000 in 1947 from 2.4 million in 1945. On the day the Japanese surrendered in August 1945, there were 218 combat groups in the Army Air Force and 70,000 planes. One year later, there were 52 groups—only two of which were considered combat-ready. The airplanes that American factories had churned out were parked end-to-end in the desert, sold to other countries or junked.

Never in history had one nation held such a strategic advantage over the rest of the world as the U.S. did in 1945, and never had a country been so reluctant to wield it. To many, the well-earned peace dividend appeared incontrovertible. Intelligence estimates assured the West that the Soviets would not be able to develop their own atomic weapon for at least 10 years. But a series of events quickly changed the strategic map.

On Aug. 19, 1949, the Soviets successfully tested their first atomic bomb, years before U.S. intelligence believed they would. Six weeks later, Mao Zedong’s communist army took control of China. Eight months after that, the North Koreans crossed the border and quickly crushed U.S. and South Korean forces. Things have a way of changing when you least expect it.

One year after World War II, the U.S. had placed its strategic nuclear advantage in the hands of a new entity called the Strategic Air Command (SAC). It made sense to hand the country’s nuclear punch over to this new branch of the Air Force, since only that service branch had the delivery system and prior experience. The B-29s of SAC were meant to so petrify any foe that they would never consider an attack on the U.S. The reality was that the new command was a shockingly disorganized, ill-equipped, nonfunctioning organization. Worse, no one seemed to care.

In 1948, the commander of SAC was replaced by Gen. Curtis LeMay, who had proven himself the ultimate problem solver in World War II, first in Europe and then in the Pacific. LeMay immediately understood the severity of the problem. He also comprehended the constantly changing geopolitical landscape.

So he walked into his office in Omaha, Neb., on one of his earliest days on the job and ordered every single bomber in SAC to take off immediately and electronically “bomb” Wright-Patterson Air Force Base in Dayton, Ohio.

Compared with a real war, this should have been a cakewalk. Crews would not have to fly over an ocean, nor would they be flying into unfamiliar or unfriendly territory. Everyone knew Wright-Pat. It was a relatively short, peaceful distance away. The control tower in Dayton would be able to track the trajectory of each plane’s “bombs” by radar.

But it turned out that many of the planes couldn’t even take off. The best mechanics had left the service for higher-paying and easier civilian jobs after the war ended, leaving SAC’s planes in woeful condition. Of the planes that could get to Dayton, not one was able to hit the target. Not one. For obvious reasons, the results were kept classified.

Seven years earlier, when the Japanese struck at Pearl Harbor, the U.S. had two large oceans that gave it the necessary time to build the armed forces it needed to win World War II. In 1948, America’s enemies still lacked the technology to threaten the mainland—Soviet missiles didn’t yet have the range—so LeMay still had time to radically reconstruct SAC. By the time he left his command in 1957, he had transformed it into the most efficient and deadly military organization ever.

The Dayton lesson serves as a cautionary tale. The next time some unforeseen event threatens the mainland as the U.S. is slashing its military budget, this country won’t have the luxury of time to rebuild what it will no doubt need.

The technical advantage that the U.S. now enjoys was never preordained. It was developed by private industry and taxpayers. And while America’s adversaries today still retain the dogma and zeal of Nazi Germany and Imperial Japan, they could soon have the technology of the Soviet Union—creating a scenario this country has never experienced.

Mr. Kozak is the author of “LeMay: The Life and Wars of General Curtis LeMay” (Regnery, 2009).