These arms are to be tailored for threat scenarios in which targets are fleeting, such as when a terrorist location has been pinpointed or a rogue nation is preparing to launch a weapon of mass destruction.

However, following the lead of the defense appropriations conference bill last month, the authorizers voiced worries about the possibility that Russia or other nuclear powers might misinterpret the launch of a conventionally tipped D-5 missile from a Trident submarine as a nuclear attack.  The misunderstanding, in turn, might elicit a nuclear-armed response, lawmakers have said.

“The conferees remain concerned about prompt global strike concepts that would employ a mixed loading of nuclear and non-nuclear systems and believe that DOD should carefully address these ambiguity concerns,” according to the report filed last week.

Under the Pentagon’s plan for conventional Trident, defense officials had intended to install 96 non-nuclear warheads on 24 D-5 missiles throughout the submarine fleet at a total cost of $503 million.  The remaining missiles aboard the boats would have carried nuclear warheads.

Marine Corps Gen. James Cartwright, vice chairman of the Joint Chiefs of Staff and a leading advocate of the conventional Trident concept, recently acknowledged that Capitol Hill concerns would likely stall the effort. 

Cartwright told Global Security Newswire he saw “signaling … from the Hill, which I don’t necessarily disagree with,” to shelve the conventional Trident and “start to focus the [research and development] on the next generation beyond conventional Trident.”

An alternative land- or sea-based weapon system might “provide either flight profile or launch conditions that would be less ambiguous,” he said.

As one such alternative, the Pentagon is working on a concept for building a new, medium-range weapon that could be launched from any of four converted Ohio-class submarines, which are to carry only conventional weapons.

However, Russia’s advanced early warning systems might similarly misinterpret the launch of this weapon as a U.S. nuclear strike using a “depressed-trajectory” Trident D-5, according to Hans Kristensen, director of the Nuclear Information Project at the Washington-based Federation of American Scientists.

Launching the missile in a flatter arc involves a shorter flight time to target and gives less time for other nations to detect and react to an incoming attack, according to nuclear weapons experts.  The shorter time lines might make for hasty and more provocative responses from Russia or other nuclear powers, critics worry.

Last week’s conference report backs existing plans to create a multiservice funding pot for an “integrated” prompt global strike program that would support an array of technologies.  The bill language does not preclude the Pentagon from spending some of $100 million in joint fiscal 2008 funds on conventional Trident components or technologies, as long as they are “applicable to other [prompt global strike] alternatives or use of the Trident D-5 as a test platform.”

It remained unclear at press time whether the report language was intended to limit the types of tests that might be conducted using the Trident D-5 missile.

Last month, President George W. Bush signed into law a defense appropriations bill providing $100 million in fiscal 2008 for prompt global strike research and development.  The House yesterday approved the authorization conference report, and it is expected to go to a vote on the Senate floor before the holiday recess.

Potential land-based alternatives for the mission include an Air Force Conventional Strike Missile and an Army Advanced Hypersonic Weapon.  Congress last month provided the Army weapon $41.7 million in unrequested funds, outside of the multiservice prompt global strike account.

Generally speaking, the lawmakers noted in the report “the value of developing conventional prompt global strike capabilities that may be needed for time-sensitive operations.”  These capabilities “would also continue the post-Cold War trend of reducing U.S. reliance on nuclear weapons by providing the president with a wider variety of non-nuclear strike options,” the document reads.

The legislators also directed the defense secretary to submit to Congress a research, development and test plan for prompt global strike technologies.  They also extended through 2009 an existing annual requirement for the defense secretary to present an integrated plan for developing, deploying, and sustaining a prompt global strike capability.

Further, lawmakers called on the Pentagon’s head of acquisition and technology to report on how the Defense Department plans to allocate its fiscal 2008 prompt global strike funds.  The defense buying czar must issue the report before the funds can be spent.