WASHINGTON — Over the past quarter century, precision guided munitions (PGMs) such as laser-guided bombs and cruise missiles have become the weapons of choice for the US military, providing a high degree of accuracy while avoiding widespread collateral damage.

And while the US and its allies have often benefited from operating in combat areas where opponents lack heavy and effective defenses, But those days are coming to an end, experts are warning. and The US needs to develop new operational concepts to maintain its precision strike advantage in the face of increasingly effective countermeasures.

"Big state powers like Russia and China are catching up," warned Deputy Defense Secretary Bob Work. "This is going to require a fundamental rethinking of how the joint force operates."

Work is overseeing an effort to develop new "offset" strategies — tactics and weapons that can offset an opponent's abilities.

"The first thing on any offset policy is to have a demonstrated capability to win the emerging guided munitions salvo competition," Work said June 22, speaking to a Rand Corp. audience in Washington. "That is job number one. This demonstrated ability to win this competition will underwrite our conventional deterrence in the 21st century, and if we don't have it, we are going to be faced with a lot of problems that we do not want to face."

He pointed out that current PGM countermeasures are simply too costly, which is why the Pentagon is investing in the research and development of cheaper alternatives, such as directed energy or electromagnetic railguns.

Work's warnings were echoed the next day by Mark Gunzinger and Bryan Clark, authors of a new report from the Center for Strategic and Budgetary Assessments that examined the future of precision strike warfare.

An enemy with effective countermeasures against platforms — generally aircraft or ships — or individual PGMs will reduce the effectiveness of precision strike weapons, Gunzinger noted. A US military accustomed to operating in a permissive environment, where "pretty much 100 percent of its PGMs would arrive on target" and where strike planners often think of how many targets can be hit per aircraft sortie, might see a significant drop in effectiveness, to maybe 50 percent.

That in turn would require lead to a drastic increase in the number of PGMs needed per target, Gunzinger said, a concept called precision plus mass. Better defenses mean more standoff weapons will be used. "But such weapons are much larger, more expensive than direct attack munitions. So fewer weapons can be carried."

The result, said Clark, "is that individual weapons are not going to be able to arrive at their intended targets."

The answer isn't just to buy many more PGMs, the two said, but rather to shift to new operational concepts combined with the development of new technologies.

One suggested alternative, Clark said, is to conduct large-scale strikes from lower threat areas, including from undersea platforms such as cruise missile submarines, and using more bombers.

"Today we do a lot of our strike missions from relatively short ranges, which could be within cruise missile range of the enemy," Clark said. "So our first concept talks about shifting to long-range strike."

Among the benefits, he noted, would be reduced risk of enemy attacks. But longer aircraft missions would reduce lead to reduced sortie rates, although offset by using larger strike aircraft with bigger payloads. Such an approach could mean a shift in the way smaller strike fighters are used, returning to something like the World War II long-range bomber escort role.

"Strike fighters might not be the best platform for long-range strike," Clark noted, as the one- or two-seat aircraft "can't operate at 2,500-mile ranges. So the missions of strike fighters may change to becoming primarily counter-air, defending air bases and long-range bombers."

Long-range, 2,600-mile strike missions ranges in turn lead to opportunities for cluster basing, Clark said, referring to a US Air Force concept of airfields located close enough to provide mutual air and missile defenses.

Another approach involves operating ship-based US Marine Corps F-35B short-takeoff/vertical landing (STOVL) joint strike fighters from small, expeditionary airfields, relocating those forces every few days. STOVL fighters could also take advantage of small forward air refueling points for further dispersed operations.

Problems with cluster basing or distributed STOVL operations, Clark said, include more complex logistics to support more bases, and command and control of dispersed forces in degraded communications environments.

Gunzinger and Clark also offered up a tunneling concept, where stealth platforms such as submarines or stealth bombers move in to deliver large numbers of small, short-range decoys and inexpensive PGMs that would temporarily deplete an enemy's defenses. More effective PGMs carried by less stealthy platforms could then swarm in to deliver strikes before an enemy can recover.

"We need to look at both kinds of PGMs — expensive and cheap," Clark urged, noting that approach "is not something DoD does well."

The chief challenge with the tunneling concept, Clark said, would be coordinating strike operations across a variety of platforms, domains and individual weapons.

A key recommendation is to increase the standoff range for penetrating strike platforms.

"We're advocating short-range standoff" — no less than 100 nautical mile-range — "for our penetrating strike platforms," Gunzinger said. "Today we have more 600-mile standoff weapons, such as CALCMs [conventional air-launched cruise missile] and JASSM-ER [joint air-to-surface standoff missile-extended range].

"But there may be a 100-to-400 nautical mile sweet spot for standoff attack PGMs," he added. "Today only JASSM is in this range band."

New, medium-range weapons also could be produced by modifying direct attack PGMs with inexpensive rockets or motors to extend ranges, Clark said, along with increasing the mission functionality of some standoff weapons. New weapons should also be developed, but that would take time.

But the new weapons would also have the advantage of being relatively efficient, "small enough to not take up huge amounts of weapons bay space but also have effective range."

Other recommendations to increase the probability of arrival percentages for PGMs and salvo sizes include developing PGMs with brilliant submunitions to strike multiple targets with one weapon; miniaturizing PGMs to increase salvo sizes or employ swarming tactics; new PGMs specialized to hit hard or deeply-buried targets; and new high-speed hypersonic weapons able to avoid most defenses.

A possible sweet spot for the latter, Gunzinger said, might be a Mach 6 air-breathing weapon similar in size to the JASSM, able to fit in bomber weapon bays.

"Our current weapons mix is not optimized for some of these recommendations," Gunzinger acknowledged, "and it's going to be challenge in this fiscal environment."

But, he added, "we need capabilities that help us bend the curve back in our direction."

The full report can be downloaded at http://csbaonline.org/

Aaron Mehta contributed to this report.

Email: ccavas@defensenews.com

Christopher P. Cavas was the naval warfare reporter for Defense News.

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