To recapitalize its aging aircraft with new replacements, the U.S. Air Force has embarked on a strategy of retiring legacy aircraft now and “investing” the budget savings for new aircraft in future years. The Air Force plans to retire aging F-15Cs, F-16s, B-1s and B-2s with F-35s, Next Generation Air Dominance fighters, B-21s and F-15EXs. This strategy may look attractive on paper, but past attempts show that it doesn’t work in practice.

Here’s why: Budget savings from retiring current aircraft are in operations and maintenance accounts, but budgets for new aircraft are in research, development and acquisition accounts. Congress will readily approve current-year operations and maintenance reductions (not savings), but cannot promise future appropriations in the more competitive and more scrutinized research, development and acquisition accounts. The two are not fungible.

Moreover, Congress does not issue IOUs to the Air Force, nor would it feel compelled to honor them even if issued. The Air Force has learned these lessons the hard way. Three recent examples dramatize these points.

The B-1 and B-2 bomber fleets have been reduced significantly from planned numbers. High cost of operating the original fleet of 100 B-1 bombers forced the Air Force to reduce the numbers incrementally to only 44 with the most recent reduction of 17 this year. Congress has intervened to prevent any further B-1 retirements until B-21s are delivered to replace them. There are 21 B-2s today, a far cry from the planned buy. Together, these retirements of B-1s and congressional cuts of B-2s create a gap in Air Force bombers until the B-21s arrive.

In 2009, the Air Force established a goal of 381 F-22 Raptors, but Congress annually whittled the number down to 187 with an understanding that it would fund enough F-35As annually to compensate. But Congress continues to reduce the planned number of F-35As to less than half. Now, the Air Force plans to divest the fleet of F-22s in favor of an undefined Next Generation Air Dominance aircraft.

The Air Force planned to buy 180 F-15EX fighters to replace worn-out F-15Cs in homeland defense and overseas. This “divest to invest” plan is already falling apart. Congress is cutting the number of F-15EXs in half — insufficient to replace the retiring F-15Cs one-for-one. Yet, defense of the homeland is the No. 1 priority in the National Defense Strategy.

Every time the Air Force trusts Congress to provide next-generation aircraft to replace obsolete, current-generation aircraft, it ends up on the short end of the stick with an insufficient, hollow next-generation stable of aircraft.

Another negative impact is that every “divest to invest” program creates a gap in capability between retirement and replacement. Most of the B-1 fleet was retired without replacement. The already insufficient F-22 fighter fleet was reduced further before F-35As were delivered to replace them. Aging F-15Cs will retire before F-15EXs are produced and delivered. The retirement of F-15s, F-16s, B-1s and B-2s before replacements are delivered will create large gaps in both numbers and capability at a time when threats in the Indo-Pacific region are increasing.

Promising next-generation capability with savings from retiring legacy aircraft may be a clever way to justify “divest to invest,” but it has proved to be a foolhardy mission.

A better strategy, albeit more difficult to convince Congress to fund, is to replace aircraft one-for-one, simultaneously retiring old aircraft only when its new replacement arrives on the flight line. To be sure, while simultaneous replacement will prevent both reduced force size and capability gaps, advocating and defending it will be a herculean task.

Nevertheless, Air Force leaders can craft a solid set of arguments, bolstered by past experience, that simultaneous replacement best protects force size and the continuous readiness of air power to confront growing threats.

“Divest to invest” may have been a workable strategy years ago when global threats were less severe. Today, however, divesting now in the hope of recapitalizing years later is too risky and can invite attacks by adversaries in the interval when our forces are weaker. Simultaneous retirement and replacement should replace “divest to invest” as the best way to build the future Air Force.

Retired Gen. John Michael Loh served as U.S. Air Force vice chief of staff and led Air Combat Command.

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