The Pentagon is preparing to press Congress for the authority to build a $503 million conventional version of the nuclear-armed Trident submarine-launched ballistic missile amid considerable concern about the proposal, particularly among influential Democrats, according to defense and congressional officials.

Marine Corps Gen. James Cartwright, the head of U.S. Strategic Command, is expected to pitch the idea in March 16 testimony before the Senate Armed Services Committee. On March 29, he is slated to appear before the committee's panel on strategic forces, where he will likely face additional questions about the new project.

Lawmakers skeptical of the effort reportedly include Sen. Daniel Inouye (D-HI), ranking minority member of the Senate Appropriations defense subcommittee and a longtime opponent of a similar modification the Navy has proposed in past years.

The Pentagon has requested $127 million for the effort in fiscal year 2007, and is also expected to seek millions of dollars in additional funds in a forthcoming reprogramming request to get the project started this year ( Inside the Pentagon, Jan. 26, p1).

The conventional Trident missile would be capable of hitting a fleeting target -- such as an enemy nuclear weapon being prepared for launch or terrorist leaders in an underground facility -- without using a nuclear warhead that runs a higher risk of killing innocent civilians nearby, according to a senior defense official.

The Navy proposes to modify its D-5 missile with two different conventional warheads: a standard “slug” useful in penetrating buried targets and a “flechette” designed to attack larger targets on the surface, the official told reporters at a March 7 meeting. To compensate for a decrease in energy compared to a nuclear weapon, the service would also modify the Trident with a maneuvering capability that would increase its accuracy.

The project is aimed at giving the Pentagon an initial “Prompt Global Strike” capability in which a target can be disabled or destroyed within one hour of an order to launch, defense officials say. The submarine-launched missile is expected to have a flight time of just 12 to 24 minutes and could hit targets up to 6,000 miles away with an accuracy of 10 yards, said the senior official, who spoke on condition of not being named.

Without naming potential targets, the senior defense official said the Pentagon has in mind potential adversaries that may be “below the equator” or “in the large land masses of Asia [or] the Middle East [and] all the way up to the Baltics.”

In attacking such targets, the Pentagon wants to avoid using a weapon that would “overfly” other nations -- raising diplomatic and military concerns about respect for other nations' sovereignty -- or might appear threatening to other nuclear weapons powers like Russia or China.

“A mobile platform” like a submarine “allows you to move to areas where you can have the lowest risk of having to involve a third party,” the official said.

However, critics on Capitol Hill and elsewhere contend a submarine-launched conventional missile creates dangerous international “ambiguity” and raises overflight concerns of its own.

Ballistic missile experts question whether a Trident missile would overfly Russia, given that a ballistic missile submarine typically remains in one of four alert patrol areas just off Russian coasts. Moreover, debris from a Trident launch -- rocket stages the missile sheds as it flies to its target -- might fall on Russia, they say.

To lawmakers, perhaps the most attractive alternative to the Trident modification might be a notional land-based conventional ballistic missile, officials say. A conventional missile based on the U.S. coastline in Florida or California -- separate from nuclear-tipped ICBMs on alert in Midwest silos -- might provide a quick-flying and less problematic alternative to submarine-based weapons, according to critics of the Trident concept.

But the senior defense official says a land missile based on a U.S. coast still would have to traverse the North Pole and Russia to reach its targets, potentially leading to a crisis born of misunderstanding, the senior official told reporters. A land-based alternative “is not really well suited in basing for what we would want to do and the targets we would want to hold at risk,” the official said.

“If you want to get to any of those [target] areas, you'll have to go over other people and you'll have to go extremely long distances,” the official said.

But some ballistic missile experts contest the Pentagon assumptions, saying a land-based weapon launched from a coast would not have to fly over the North Pole or Russia. Rather, it could be programmed to take a less ambiguous flight path to its target, thus mitigating the possibility of triggering an unwanted Russian response, some defense analysts say.

Further, critics of the Trident idea say overflight of other nations is not an issue with a ground-based missile based on a U.S. coast because it could launch over an ocean, traverse space, and re-enter the atmosphere inside the country being targeted.

“We have a right to overfly other countries if we are in space,” said one defense analyst.

Asked to respond, a senior official at Strategic Command said the Trident submarine “offers a flexible platform for delivering conventional ballistic weapons from a large number of launch locations. Additionally, it affords us the opportunity to deliver a needed capability to the warfighter quickly.”

The official's March 8 e-mailed response to questions did not address the issue of space overflight directly.

Defense analysts also take on a Pentagon assertion that missiles based at a U.S. coastal facility would present launch debris problems. Debris from discarded rocket stages would fall into the ocean rather than threaten any population centers, these analysts say.

However, the senior official meeting with reporters on March 7 maintained that in using the Trident, it is “much easier to take care of the launch debris [from] the rocket stages. You can set that up to fall in the water.”

As a missile follows its ballistic trajectory back into the atmosphere and nears its target, it again sheds debris. Here, too, the submarine-launched alternative presents an advantage, according to this senior official. The sea-launched missile will be capable of maneuvering to minimize the possibility that end-stage debris will threaten innocent civilians in the area, the official said.

The current Minuteman III ICBM would not be as ready as the Trident to accept a maneuverability upgrade that increases accuracy and helps avoid debris damage, the senior official said.

“We're hoping to get another 10 to 15 years out of [the Minuteman] but it's not in production,” said the official. “It is a '70s and '80s design. It is not built to have the accuracy improved to the levels that we're seeking here. You'd have to do a major rebuild of the asset to do that.”

Conversely, “with a sea-launched [missile like] the D-5 . . . it is much simpler to just install the accuracy upgrades for a missile that's in production and available right now,” the official said. “It was designed for this and it's not a big effort to stick that in.”

However, says one critic, “No one has ever proposed [using] Minuteman for a conventional ballistic missile.” Rather, a land-based missile concept widely circulating in the defense community envisions using a Minotaur III missile, which comprises a commercial front end, three excess MX missile boosters and a commercial guidance system. The Minotaur III cannot physically support a nuclear re-entry vehicle and could be readily subject to Russian inspection to ensure START treaty compliance, according to advocates.

And, some experts say, this land-based missile could use the very same tailkit proposed for the Trident to increase accuracy.

Another question under debate as Cartwright prepares to testify before Congress is whether a sea- or land-based missile could arrive at its target more quickly.

Using the Trident, “you can have the shortest flight times so that if somebody is trying to hold their neighbor at risk with a short- or medium-range ballistic missile, you've actually got the time lines to do something about it,” the senior officer contends.

Yet critics challenge the notion that a submarine-launched missile is, in fact, the quickest option to respond to a quickly emerging threat. They say command and control remains cumbersome when communicating launch orders to Trident submarines, which remain submerged on alert to hide their exact location. The submarines take time to rise to a depth at which they can receive transmissions, and communications with the subs remain slow, experts say.

Asked to clarify how much time the communication of targeting orders adds to the Trident's launch sequence, the senior official at Strategic Command told ITP the details are secret. Instead he stated simply that the conventional Trident modification “will provide America the ability to defeat a diverse set of threats on short notice.”

Upon receiving launch orders, a submarine inside an ocean alert area near Russia would likely have to steam toward its target to get within range and minimize overflight concerns, outside experts say. This could take hours or days, depending on the location of the alert area and the target, according to experts. Once within range, the submarine must rise to launch depth and stabilize, processes that could add yet more time to getting a weapon on target.

Senior defense officials and Trident critics alike emphasize minutes could make a difference in heading off disaster. One possible scenario in which a rapid response would be required is if North Korea has already launched one nuclear weapon and two more are being readied for launch, says one defense expert.

“Don't you want to kill the other two on the launch pad?” asks this source, who contends a land-based missile can be launched inside of the time it could take a submarine to receive orders and move within striking distance of a target.

The senior Strategic Command official said that although the precise locations and operating patterns of Trident submarines remain classified, the submerged boats “patrol very large areas of the ocean during their deployments.”

This “flexibility is one of the key attributes that make the [Trident submarine] an effective platform to launch a conventional Prompt Global Strike” weapon, he added.

“It is true that a Trident missile cannot cover the entire surface of the Earth from any one point in the ocean,” the official said. How long it might take for a submarine to get in place to launch “is as varied as the number of possible targets against which the weapon might be used, as well as the number of possible launch locations,” he said.

The official also touted the survivability of the stealthy submarines on which the conventional missiles are to be based.

“Additional benefits of using [Trident subs] for this mission are survivability and stealth,” the senior Strategic Command official said.

But he declined to compare the notional survivability of land-based ballistic missiles. If located at Vandenberg Air Force Base, CA, land-based conventional missiles could be protected by missile defense interceptors the Pentagon is stationing there, according to advocates of this alternative concept.

The senior defense official who met with reporters earlier in the week raised additional objections to land basing for the conventional Prompt Global Strike missile. Such an alternative would present “problems of treaties and what we've agreed to do and inspections,” he said. The official minimized the possibility that treaty problems would arise with the conventional Trident concept.

The Pentagon would “keep [the Trident] subject to the treaties, so [Russian officials] can look at it,” the senior official said. “They can go inspect it. They can see where it is. They can see what it looks like. They can see whether it's changed or not. [Let's] keep all of those things up above board.”

Defense experts say this policy would represent a major change for the Navy, which has not allowed Russian inspectors aboard its Trident submarines to date.

Of all the questions raised by critics, the one with “the most credibility” is concern about international ambiguity if a Trident is launched, the senior official said at the meeting with reporters.

Defense officials and experts worry other nuclear weapons nations with early-warning surveillance capability like Russia or China might mistake a conventional launch for a nuclear weapons attack. Ambiguity might arise because the submarines will carry both nuclear and conventional versions of the Trident, which could appear identical in flight to surveillance satellites these nations field, the senior official explained.

“If you launch one of these conventional ballistic missiles, will it be interpreted as having a nuclear warhead and therefore elicit a response that you did not want, [namely] a nuclear response?” the official said.

But the military has longtime experience fielding both conventional and nuclear weapons on the same platforms, including ships and bombers, which minimizes the risk of a mistaken nuclear launch, the senior official said. And the United States will continue a “robust” test launch notification regime with Russia that helps reduce potential miscues, according to the official.

Some lawmakers also wonder why the Pentagon cannot instead use existing weapons for the Prompt Global Strike mission, like bomber aircraft or Tomahawk Land Attack Missiles off of Navy ships. Existing cruise missiles or bombers are just not fast enough, the senior official responds.

The Pentagon would need “plenty of warning [and] plenty of time” to get bombers or cruise missiles within range of their targets, the official told reporters.

For bombers, “the best you're going to do that in is a day, unless you're just absolutely lucky and they pick someplace next to where you're based,” the official said.

Furthermore, “you've got to get the overflight rights” for traversing other nations en route to the target, said the senior official, adding, “You might be willing to violate that in an extreme situation.”