Word came on Thursday that the Air Force has grounded all of its KC-135 tanker aircraft because of a defective pin that could result in the loss of a part of the tail section of the aircraft while in flight.

The Air Force has a fleet of 396 KC-135s, almost all of which are old and worn out. About 243 of them are operated by the Air Force Reserve and Air National Guard. (The Air Force also has about 60 KC-10 tankers, derived from the McDonnell Douglas DC-10.)

This column has been arguing — for almost 18 years — that one of our most urgent defense needs is to replace the KC-135 with a new tanker.

In the March 2005 edition of The American Spectator, I explained the importance of the KC-135 by quoting then–Air Force Chief of Staff Gen. John Jumper.

As Gen. Jumper explained to me then:

We are a global air and space power because of these tankers.… The first thing that happens in any contingency is that you put the tanker air bridge up there. We deploy tankers to places such as Spain, Hawaii, Guam, and their sole purpose is to get large numbers of transport aircraft halfway around the world without stopping.

If the tankers aren’t on station, bombers and fighters can’t reach their targets, and cargo aircraft can’t deliver troops and the supplies they need to have in order to enter and sustain combat.

It boils down to this: no tankers, no superpower.

The KC-135 is a military version of the old Boeing 707. The first ones were delivered to the Air Force in 1956 and achieved initial operational capability in 1957. The aircraft continued to be built, and the last delivery was in 2005.

Other aircraft the Air Force also depends on — such as the E-3 Sentry (AWACS), E-8 JSTARS battle management aircraft, the RC-135 reconnaissance aircraft, and the WC-135 radiation detection plane — are also built on the old Boeing 707 airframe and, presumably, grounded as well.

As Gen. John Handy — then commander of Air Force Mobility Command — told me for the 2005 article, “As these aircraft age out, they’re not useful in any wartime scenario.” Since 2005 and to this day, the KC-135s have served as the workhorse tanker. All or most of them have “aged out” from constant usage, just as Handy predicted.

The Air Force has been trying to replace the KC-135s for about 20 years, but it couldn’t — while John McCain was in the Senate — convince Congress to give it the money to do so. At one point, the Air Force got so desperate that it tried to lease new tankers from Boeing. McCain killed that plan as well. (The Air Force didn’t distinguish itself in that one. A senior acquisition official, trying to get a job at Boeing, increased the lease cost significantly. She was sentenced to nine months in prison. A Boeing executive was also convicted of criminal activity.)

About a dozen years ago, the Air Force tried to award a contract to Airbus for new tankers, but the Government Accountability Office overturned the award because the Airbus was too heavy, slow, and underpowered to perform the vital maneuvers required of tanker aircraft. The Airbus was a dumb choice. It remains to be seen if the new Boeing tanker will be much better.

Boeing finally won the contract to replace the KC-135s several years ago, but its new tanker — the KC-46 — is still not operational. It has technical problems with the “boom” — the crane-like device that connects to the aircraft being refueled and pumps fuel into the receiving aircraft — along with a number of other major issues.

As usual, the problems result from over-engineering the new tanker. For example, in the older tankers, the “boomer” — the guy who “flies” the boom and connects it to the receiving aircraft — sat in the back of the tanker and viewed the receiving aircraft directly. In the KC-46, the “boomer” sits in the warm cabin drinking coffee and guides the boom to the receiver by watching it on television. It works, sort of, but not well enough to qualify the KC-46 to refuel A-10s.

So it all comes down to the ancient KC-135 having to meet the Air Force’s needs for the foreseeable future. And now it’s grounded for days, weeks, or months until the problem with the tail section is inspected and repaired.

The grounding of the KC-135s — and the E-3 AWACS and E-8 JSTARS — presents an opportunity to Chinese President Xi Jinping that he may not be able to resist. It’s an opportunity to conquer Taiwan without American interference.

If Xi can mount an attack on Taiwan within, say, the next month, his attack could not be opposed by any significant number of U.S. Air Force aircraft. Because the Chinese have designed their air, missile, and naval forces as “area denial” forces — precisely to keep U.S. Navy aircraft on carriers from reaching the contested zone — our Navy would probably be unable to get its carriers in range of Taiwan.

It’s unlikely — but possible — that Xi will be able to act quickly enough to attack Taiwan while the KC-135s are still grounded. The Air Force has received delivery of 62 KC-46s from Boeing, but that’s a long way from replacing — i.e., achieving initial operational capability — the nearly 400 KC-135s that have been grounded.

The longer the KC-135s are grounded and the longer it takes Boeing to get its act together on the KC-46, the longer Xi’s window of opportunity will remain open.

At this point, there isn’t much that can be done to solve this critical problem. The Air Force should kick Boeing in its tail — hard — to speed up deliveries of aircraft that meet its standards, but that probably won’t be enough to get the new tankers in the air quickly enough to close Xi’s window of opportunity.