An antisubmarine rocket launches and releases a weapon into the water. Hearing the water entry with its sonar, the submarine crew fires a nuclear-armed torpedo at the USS Bedford. Both ships maneuver vainly, unable to avoid or counter the incoming weapons that destroy them.

A similar confrontation between ships today might yield a similar, if non-nuclear, result. But the U.S. Navy is determined to fight fire with fire by developing an anti-torpedo torpedo (ATT), a weapon designed to enable surface ships and submarines to destroy incoming submarine-launched torpedoes.

The small-diameter ATT currently under development also shows promise as a multimission weapon, useful against submarines and small ships and light enough to be deployed on unmanned vehicles.

A submarine-launched torpedo, typically 21 inches in diameter, is difficult to counter and evade. It travels at relatively high speeds (more than 40 knots) -- providing very little reaction time -- and is difficult for a surface ship to spot and track. No existing weapons, such as naval gun systems, are effective against torpedoes without a lucky hit.

Surface ships can deploy the Nixie, an acoustic jammer towed behind the ship, to confuse an incoming torpedo. And submarines can eject countermeasures such as noisemakers to decoy incoming homing torpedoes away from their target.

The Navy now is procuring similar expendable countermeasures that can be launched from a surface ship.

The ATT is 6.75 inches in diameter, 105 inches long, weighs approximately 200 pounds and is powered by a stored chemical-energy propulsion system -- which uses steam created by chemical reaction -- similar to that used in the Navy's Mk50 lightweight torpedo. It is designed to operate in the noisy, turbulent wakes of ships, where it could intercept wake-homing torpedoes.

The ATT could be adapted to be launched from the common surface-vessel torpedo tube launcher -- currently used to launch larger antisubmarine torpedoes -- and from the standard Rolling Airframe Missile launcher installed on many surface combatants.

“We just have to get it clear of the ship, [which is] just a matter of kicking it over the side into the water in a timely manner so it can go after the target,” said Capt. Mark W. Bock, the Navy's program manager for undersea defensive warfare systems.

Later this year, the Navy will test an ATT prototype to ensure its compatibility for surface and subsurface launch. The subsurface launcher would be mounted external to the submarine's pressure hull.

“I am confident that the submarine force will invest in this capability,” Bock said, noting he does not expect the ATT to replace the heavyweight and lightweight torpedoes in service. However, the ATT could give a submarine commander more options from which to choose. The ATT also could serve as an antisubmarine weapon -- a variant called the Common Very Lightweight Torpedo -- fired from the same launcher.

The lightweight torpedo variant would have a smaller warhead than standard submarine-launched torpedoes. But “analysis shows that it is still lethal enough to inflict significant damage on a large percentage of targets of interest in the foreseeable future,” Bock said.

The Common Very Lightweight Torpedo could be carried by smaller platforms such as unmanned aerial vehicles. The Navy is considering fitting it to the RQ-8B Fire Scout unmanned aerial vehicle. The Fire Scout, which is similar to a helicopter, is being developed to operate from the Navy's future fleet of Littoral Combat Ships. The very lightweight variant also could be adapted for MH-60R helicopters. In these roles, it would be renamed the Compact Rapid Attack Weapon.

The Navy made abortive efforts to develop ATTs during the naval build-up of the early 1980s. One example, a version of the service's standard Mk46 lightweight, 12.75-inch-diameter antisubmarine torpedo, designed for launch from aircraft and surface ships, was modified as an ATT but failed its operational evaluation -- its final exam -- in 1994 and was canceled.

What makes an ATT achievable now are advances in the “miniaturization of electronics and the subsequent increases in microprocessor computational capability,” said Bock. In countering an incoming torpedo, “the ATT must be able to very rapidly process all of the acoustic information availability and make timely maneuvers in order to intercept the incoming threat.”

Currently, the ATT is being developed under sponsorship of the Navy's program executive officer for submarines by the Pennsylvania State University Applied Research Laboratory (ARL Penn State) -- one of the Navy's four university affiliated research laboratories.

Working with the Naval Undersea Warfare Center in Newport, R.I., and the Naval Surface Warfare Centers in Indian Head, Md., and Crane, Ind., the laboratory is conducting a series of in-water tests of the 6.75-inch-diameter ATT this year as one element of the multifaceted Surface Ship Torpedo Defense system.

Bock noted several challenges in designing an effective ATT to operate in the noisy acoustic environment of the wake of a ship. An ATT's very short mission timeline requires quick detection, decisions and maneuvers. Precise homing is required to place the ATT's warhead close enough to destroy the incoming torpedo, a difficult requirement when the ATT and torpedo close rapidly on each other. In addition, the weapon must detect and engage salvos of incoming torpedoes simultaneously, and should have an option for automatic launch.

“Putting very high-performance technology and subsystems into a very small package makes everything a challenge,” said Leo Schneider, associate director of the Undersea Weapons Office at ARL Penn State. “Doing all of this in an affordable package [is] not always consistent with high performance in design. The Navy can't pay what they've paid for torpedoes in the past.”

“We've exploited the commercial market as much as possible,” said Russ Burkhardt, head of the Technology Development and Transition Division of the Undersea Weapons Office at ARL Penn State. Digital engine control computer technology, such as the type that controls ignition and other functions in modern automobiles, is being adapted to the ATT, he said.

Employing a torpedo to intercept a torpedo is akin to the challenge faced by surface-to-air missiles designed to intercept cruise missiles, said Schneider.

“The characteristics of the intercept mission don't change,” he said. But underwater, “the low sensing rates with the speed of sound” make it more of a challenge for a weapon equipped with an acoustic sensor, as opposed to an aerial weapon equipped with a radar or electro-optical device sensing at the speed of light.

Bock declined to comment on the capabilities of the ATT versus a rocket-powered high-speed torpedo such as the Russian-designed Shkval, which reportedly can reach speeds of 220 miles per hour.

“That's not currently part of the requirement we're building against,” he said.

Bock also declined to discuss funding levels for the ATT. Navy budget documents show that the service allocated $54.6 million, $53.1 million and $40 million in fiscal years 2005, 2006 and 2007, respectively, for development of the Surface Ship Torpedo Defense system, of which the ATT is a part. He said there will be a “full and open competition to build the ATT.

“The ATT is on schedule as major subsystem testing nears completion,” he said. “We are planning initial operational capability for the ATT mission in fiscal year 2012.”