Congress this week may kill one of America’s most iconic, and still vital, airplanes. First introduced in the mid-1950s, the U-2 high-altitude intelligence-gathering plane has played a pivotal role since the Cold War. Now, it is on the chopping block, slated to become another casualty in Washington’s defense-budget Kabuki. Recent congressional testimony and number-crunching make the case that Congress should preserve the U-2, and with it America’s continuing dominance of aerial reconnaissance.

The U-2 has survived nearly six decades of service. Designed by legendary Lockheed engineer Clarence ” Kelly ” Johnson —who founded the company’s equally legendary “Skunk Works” advanced aircraft-development division—the first U-2s were delivered by Lockheed in July 1955, just eight months after the final approval of the project.

The technological feat of creating a single-engine glider-like aircraft that could fly at 70,000 feet, nearly half-again as high as any existing airplane, remains one of the most impressive accomplishments in U.S. aeronautical engineering. Today’s budget hawks, however, would be even more impressed to know that Lockheed delivered the original batch of U-2s for 15% less than the agreed-upon price of $22.5 million for the first 20 planes.

Operated by the CIA, the U-2 flew with impunity over the Soviet Union and China until May 1, 1960, when on the very last planned overflight of the U.S.S.R. Francis Gary Powers was shot down and captured, provoking a crisis in U.S.-Soviet relations. Two years later, Air Force Maj. Rudolph Anderson was shot down and killed over Cuba during the missile crisis.

While it easily could have become obsolete in an era of spy satellites, the U-2 over the decades has evolved to remain one of the most precise intelligence, surveillance and reconnaissance platforms in the U.S. arsenal. Now operated by the Air Force, the 27 operational U-2s maintain unparalleled cameras and optical sensors. The Air Force has also modernized the U-2’s electronic-warfare capabilities and data links since 2001, as well as other imagery systems. Its airframe is expected to be usable until 2040. The “Dragon Lady,” as it is nicknamed, is able to reach transcontinental targets on short notice, unlike satellites, which is why it remains a favorite of the intelligence service and combatant commanders alike.

In the current round of budget cuts, the Air Force initially favored keeping the U-2 and instead retiring 18 of its mid-level RQ-4 Global Hawks, given that those highly touted drones did not have as powerful an optical sensor, cost more than the U-2 to fly, and cannot be flown in adverse weather. This year, however, under congressional pressure, the Air Force did an about-face, offering up all the U-2s in exchange for upgrading the Global Hawks.

It is time to go back to the original plan. From a strategic perspective, the U-2 wins out over Global Hawk. The Dragon Lady still can fly at least 10,000 feet higher than the drone and maintains superior cameras and optical systems. That is why Army Gen. Curtis Scaparrotti, commander of U.S. Forces Korea, testified before the Senate Armed Services Committee last month that the U-2 provides better early warning of a potential North Korean threat. So if it is a matter of avoiding strategic surprise during tense crisis situations, such as in Ukraine or North Korea, the U-2 comes out on top.

What about cost savings? It will take at least $1.77 billion over 10 years, under current plans, to convert all the Global Hawks to carrying current U-2 sensors. Since the cost savings of mothballing the U-2 fleet is estimated at $2.2 billion, that’s a savings of only $430 million.

The Global Hawk’s base flying cost may have come down and it may be able to fly longer than the U-2, but it cannot fly better. If Ukraine has reinforced any lesson, it is to be as prepared as possible to mitigate risk around the globe and avoid surprise. Undoubtedly, one day the U-2 will no longer be able to do its mission better than remotely piloted drones. But that day is not here yet, and it is more cost effective and operationally wise to use the best airplane for the job.

Mr. Auslin is a resident scholar at the American Enterprise Institute in Washington, D.C., and a columnist for WSJ.com.