The signal sounded like crickets chirping, but the encoded message transmitted from the camp atop the frozen Arctic Ocean was music to the ears of the USS New Hampshire submarine crew.

Using a digital Deep Siren tactical messaging system and a simpler underwater telephone, officials from the Navy's Arctic Submarine Laboratory at the camp last Saturday were able to help the submarine find a relatively ice-free spot to surface and evacuate a sailor stricken with appendicitis.

The alternative would have been a ruptured appendix, or an emergency surgery on the table in the captain's dining room, said a relieved Dan Roberts, the senior chief and corpsman who handles the crew's medical needs. It would have been rough.

The low-frequency system is built by Raytheon Co, which has been working on it for several years with $5.2 million in initial seed money from the Navy.

Raytheon is the latest company trying to tackle the persistent challenge of communicating with submarines while they are traveling deep under the sea to avoid detection. Past systems have proven too complicated, and too expensive.

The new system could revolutionize how military commanders stay in touch with submarines all over the world, allowing them to alert a submarine about an enemy ship on the surface or a new mission, without it needing to surface to periscope level, or 60 feet, where it could be detected by potential enemies.

At present, submarines use an underwater phone to communicate with associates on top of the ice or with other submarines, but those devices are little more than tin cans on a string and work only at shorter distances. Submarines can also trail an antenna once they surface to periscope depth, or around 60 feet, but that makes them easier to detect.

Captain Rhett Jaehn, the No. 2 official in charge of submarine operations and the officer in charge of the ice camp 150 miles north of Prudhoe Bay, said the Deep Siren was heavily used during the exercises and played a key role in facilitating the evacuation of the sick sailor.

Improving the ability to communicate with submarines at any depth and any distance is a huge step forward, said Matthew Pesce, a former submariner who now works for the Arctic Submarine Laboratory, which organizes biannual ice exercises in the region, where submarines practice tactics and procedures.

Pesce is based in Hawaii, but came aboard the USS New Hampshire for the exercises as adviser for Arctic equipment and issues, including the Deep Siren system. He said the system worked well, but some transmissions were not received properly, possibly due to issues related to the ice, or the alignment of the submarine.

The new product could generate significant revenue for the company, said Stephen Moynahan, a senior Raytheon engineer, who came to the ice camp in early March to test how the system works under the ice cap, where varying salinity levels and long ice keels distort how sound travels.

He gave no details on the scope of possible sales, but said Britain successfully tested Deep Siren in the Mediterranean last year, proving a range of more than 100 miles. Several other countries were interested and two planned sea trials this year, he said. A variant allows a submarine to deploy a buoy that can relay messages via satellite link.

Moynahan said the new system, initially conceived by a Scottish submariner named Robert Kerr, provided only limited messaging ability, not bandwidth for transmitting huge chunks of data, but said its simplicity made it effective, especially in the current difficult budget environment.

This is a really big deal. This is a game-changing technology, said Moynahan, who served as the rifleman guarding against polar bear attacks during a visit to the camp by Navy Secretary Ray Mabus and other top lawmakers and defense officials on Saturday. No bears turned up.

Pesce said the system helped the submarine find a place to surface since locating ice-free waters in the Arctic was a little like looking upward through a straw, he said.

(By Andrea Shala-Esa, editing by Matthew Lewis)