As the U.S. Air Force faced stiff opposition in Congress to its latest attempts to kill the A-10 Warthog, it offered up a thinly...

As the U.S. Air Force faced stiff opposition in Congress to its latest attempts to kill the A-10 Warthog, it offered up a thinly veiled threat. If it couldn’t ditch the low- and slow-flying planes, the service would cut somewhere else … like its F-16 fleet.

The cuts were necessary to free up funds for the incoming F-35 Joint Strike Fighter, the Air Force argued in a April 2015 memo to the House Armed Services Committee. More specifically, if the flying branch couldn’t retire A-10s at Hill Air Force Base in Utah, it would send the base’s Vipers to the boneyard instead.

After swift criticism from lawmakers, the Air Force recalled the memo, claiming it had not cleared the paper for release.

But what the flying branch didn’t say in its message — or in public — was that budget woes have threatened the F-16 for years. A 2013 Air Combat Command historical review highlights serious concerns about what might happen to the fast-moving jets.

Between shrinking coffers imposed by caps on defense spending and the growing cost of the troublesome F-35 program, the Air Force decided to halt much needed upgrades for its F-16s. But this threatened to create new, potentially more dangerous gaps.

Air Combat Command oversees the bulk of the service’s combat aircraft, including the Warthogs and Vipers, and hopes to eventually take over the first combat ready F-35A stealth fighters sometime in 2016.

War Is Boring obtained a heavily redacted copy of the historical review via the Freedom of Information Act.

The F-16C is the Air Force’s most ubiquitous fighter and provides the bulk of the service’s combat power. In 2007, the flying branch had more than 1,000 of the single-engine fighters — more the total number of F-15Cs, F-15Es and F-22s put together.

Four years later, the 1990s-era Vipers desperately needed an overhaul, so the Air Force planned to put at least 300 jets through a so-called Service Life Extension Program.

SLEP involved replacing significant portions of the aircraft’s basic structure. Without these vital repairs, wear and tear on the wings, fuselage and other components might literally cause the jets to fall out of the sky.

On top of that, the Air Force wanted to give each of these older F-16s what it termed a Combat Avionics Programmed Extension Suite, or CAPES. While the SLEP would keep the aircraft flying safely, CAPES would ensure the jets could fight and defend themselves against a high-tech enemy.

With new radars, defensive gear, communications equipment and digital monitors, the upgraded jets would be just as capable as the newest F-16s. By using the same gear fitted to newer models — or gear already in limited production for the Air National Guard — Air Combat Command could do all this work on the cheap.

But not cheap enough.

“F-16 fleet modernization efforts continued through 2013, but eventually halted because of funding constraints,” the history explained. “4th Gen modernization became a target to pay for 5th Gen recapitalization, and this tradeoff included the F-16 programs.”

Fourth-generation jets include the F-15 and the F-16. The new fifth generation encompasses stealthier designs such as the F-22 and F-35.

In short, the flying branch axed much needed upgrades for the F-16 to keep its stealthy F-22s in the air.

But the Air Force understood that it still needed to keep its Vipers in working order. While the flying branch hopes to eventually trade in all of its F-16s for F-35s, cost overruns, delays and a host of other nagging issues means the new Joint Strike Fighters won’t be available in significant numbers for decades.

“With numerous problems in the past and on the horizon for the JSF program, the problem worried ACC staff,” the historical review noted.

The Air Force could have bought new F-16s to replace the older jets, but this would have cost five times more than just upgrading the existing planes. Yet “even if the JSF program delivered the F-35As at the prescribed rate of 80 per year, there was no possibility of filling the gap by 2040 without another aircraft,” the history declared.

The F-16s would have to soldier on one way or another.

Fast forward two years later and some of Air Combat Command’s fears are coming true. If all goes to plan, front-line Air Force squadrons will start getting F-35As within the next 18 months.

The Air Force expects two F-35As to show up at Hill Air Force Base in September. Once that happens, the branch will begin retiring the base’s nearly 50 F-16s.

But for at least another year, the F-35s will lack numerous key systems, such as the software necessary to use make use of its internal 25-millimeter Gatling gun. In January, the Pentagon’s top weapon tester cited a laundry list of serious issues that could also keep the stealthy jet from reaching its full combat potential.

In the meantime, the Vipers — as well as the A-10s — are engaged in bombing Islamic State in Iraq and Syria. After Russia invaded Crimea and sparked an international crisis, the Air Force dispatched the jets to reassure America’s NATO allies.

Unfortunately, the F-16s have been showing their age. In November 2014, an F-16 crashed into the Gulf of Mexico. In August 2015, another one of the jets went down in Germany.

While we don’t yet know the official cause of these two crashes, mechanical failure may have played a role. In the last two years, the Viper fleet has suffered additional losses linked to pilot error at home and abroad.

None of this bodes well for pilots who might be stuck flying the aging jets for another two decades or more.