WASHINGTON — With stagnant budgets on the horizon, the U.S. Air Force is hurtling toward “the most difficult force structure decisions in generations” and must cancel programs and sacrifice some of its existing aircraft inventory to prepare for a potential fight against Russia or China, the service’s top general said Monday.

A future war with either country could entail combat losses on par with those of a major conflict like World War II, Air Force Chief of Staff Gen. Charles “CQ” Brown wrote in a paper titled “Accelerate Change or Lose,” which outlines his vision as the service’s new top uniformed leader. Brown became chief of staff of the Air Force on Aug. 6.

Although the Defense Department has focused on war with an advanced, near-peer nation since 2016, Brown raised concerns that the Air Force’s sense of urgency is not strong enough and warned of potential mission failure unless the service accelerates the pace of change.

A “ruthless prioritization” of the service’s requirements is in order, he said.

“We must reframe platform-centric debates to focus instead on capabilities to execute the mission relative to our adversaries,” he wrote. “Programs that once held promise, but are no longer affordable or will not deliver needed capabilities on competition-relevant timelines, must be divested or terminated. Cost, schedule, and performance metrics alone are no longer sufficient metrics of acquisition success.”

The Air Force must be responsive to the actions of its adversaries, pivoting when necessary to stay ahead and creating technologies that can be cost-effectively operated and maintained, Brown added.

“Capabilities must be conceived, developed, and fielded inside competitors’ fielding timelines — knowing we will need to adapt and adjust over time. Innovative ideas from our Airmen need viable sustainment pathways. If we are to beat our competitors in conflict, we must also beat them in development and fielding of capability,” he said.

It’s unclear what existing capabilities could be on the chopping block, but more details on the Air Force’s path forward are expected. During a Aug. 31 roundtable, Brown told reporters that the service is working on action orders associated with his strategic vision that will be unveiled at the Air Force Association’s conference during the week of Sept. 14.

Brown’s call for rapid change could pave the way for another bloody budget rollout when the Air Force’s plan for fiscal 2022 is revealed next year.

During its FY21 budget deliberations, service leaders alluded to “controversial changes” such as fleetwide divestments, but ultimately the Air Force proposed retiring handfuls of older platforms rather than entire aircraft types.

Congress has attempted to curtail some of those changes, putting strict limits on the amount of tankers and bombers permitted to be retired each year.

Brown acknowledged that if he’s to make radical changes to force structure, he will need to have tough conversations with other Air Force and Pentagon leaders, Congress, and industry to determine where risk can be taken.

“When we work in various silos, we’re all trying to make our particular program or platform as capable as we can be. But we can’t afford all of those,” he said. The difficulty is getting “the right set of full programs” and not “a number of broken programs” that “balance the checkbook at the expense of our capability.”

Brown’s priorities for the Air Force extend beyond changes to existing force structure and modernization plans. Like his predecessor, Gen. Dave Goldfein, Brown stressed the importance of the military’s Joint All-Domain Command and Control concept, as well as increased interoperability and data sharing with allies.

Brown also hinted that a restructure of the Air Force could be forthcoming, and that the creation of the Space Force provides an opportunity to review the roles and missions of his service.

“Sometimes the model we use in the deployed environment is different than the model we use at home,” he said. “You want to train like you’re going to fight. From that aspect, we’ve got to take a look at ourselves.”