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US arms behemoth Raytheon has won a $5.2m contract to deliver its Deep Siren "tactical paging system" for submarines to the US navy.

Submarines, being underwater, are often hard to get in touch with. The only kind of radio which works at all is very-long-wavelength, which can be used to contact subs trailing special antennae provided they aren't too deep. This solution has sharply limited bandwidth and only works shore-to-ship. The only other option, historically, has been for the sub to come to persicope depth and put up a comms mast.

That was OK for the Cold War, when most of the subs' business involved independent, strictly maritime missions. Nowadays, however, the underwater warships need to get involved in modern combined operations, for which their new bosses would like to be able to reach them more easily - just like the hapless modern wage slave with his BlackBerry.

Hence Deep Siren, which is a fairly basic idea. A surface or air boss wishing to get in touch with a sub drops a small disposable buoy into the sea somewhere within a few tens of miles of the sub's location. The buoy has Iridium satcomms, allowing it to connect to the US military's Global Information Grid comms infrastructure.

From the buoy, the signal is passed on via an acoustic signal which can be picked up by the sub up to 50 miles away. The system is one-way, hence "paging system". The acoustic signal is unavoidably low-bandwidth, but then so is Iridium.

Each buoy can last for three days, including up to 30 minutes of acoustic transmissions, according to the Raytheon data sheet.

Raytheon got the job of developing Deep Siren back in 2005, and this latest contract is for delivery.

"Submarine communication protocols are much the same as they were 60 years ago," said Raytheon's Jerry Powlen.

"Integrating satellite communications with acoustic Deep Siren technology dramatically changes this paradigm by enabling a commander anywhere in the world to contact a submarine immediately regardless of the submarine's speed or depth."

In fact, the one-way nature of the link, the usually uncertain location of a submerged boat, and the unpredictability of marine acoustics would suggest that the kit may not be 100 per cent reliable. The Raytheon spec claims only "a high confidence of communicating reliably to a submerged submarine".

In many ways, you might say that the limited nature of Deep Siren indicates just how bad the existing options for communicating with submarines were. That said, Deep Siren is supposed to be just the first generation of a lot of new kit which will finally, properly bring the lone-wolf submarine captains under the heel of shore HQ like everyone else. ®

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