WASHINGTON — As advocates call on the Pentagon to buy as many as 200 next-generation bombers to counter growing threats, House legislation released this week urged the Air Force to take another look at how many B-21s commanders really need.

Both top military officials and experts outside the Pentagon have recommended the Air Force buy more than the 100 planned Northrop Grumman B-21 bombers to ensure enough aircraft are available to meet combatant commander requirements, according to the House Armed Services Seapower and Projection Forces Subcommittee's markup of the 2017 defense policy bill, released Tuesday.

The sweet spot is between 174 and 205 B-21s, independent experts told the committee, according to the legislation. Meanwhile, Air Force Global Strike Commander Gen. Robin Rand said the 100-bomber number should be treated as the lower limit of the requirement, lawmakers noted.

The legislation would direct the secretary of the Air Force to submit a report to the congressional defense committees by Feb. 1, 2017, estimating the number of B-21s needed to meet the demand signal. The report should also include a detailed transition plan that integrates the B-21 into the current bomber fleet out to 2040, according to the language.

Lawmakers also expressed concern that Congress does not have sufficient ability to track cost and schedule of the highly classified development effort. The legislation would direct the secretary to submit an initial "B-21 Development Progress Matrix" to the congressional defense committees, including milestones and metrics for measuring the program's progress.

"The committee is pleased to see progress on this program and believes that this program has stable requirements in place," according to the legislation. "However, the committee is concerned that, given the length of time associated with the [engineering, manufacturing and development] phase and the amount of resources planned for this phase, the congressional defense committees need an improved ability to track annual progress and cost throughout the development."

The legislation comes on the heels of a recent Congressional Research Service report urging Congress to take a look at whether it has enough oversight of the bomber program. The Pentagon is procuring the B-21 via the Air Force's secretive Rapid Capabilities Office, a small group inside Air Force acquisitions that handles classified programs such as the X-37B spacecraft. The RCO is exempt from many of the rules and regulations Congress usually imposes on a normal acquisition program.

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