LONDON — The Royal Navy has ordered what it says will be the largest and most complex unmanned submarine operated by a European navy in a deal aimed at strengthening Britain’s ability to protect undersea cables and pipelines.

The contract, secured by M Subs, a small specialist underwater vehicles maker based in Plymouth, South West England, should see the 12-meters-long submarine delivered to the Royal Navy in two years.

Announcing the £15.4 million ($18.9 million) deal Dec. 1 the Ministry of Defence said the procurement is the “first step in developing an operational autonomous submarine that will work side-by-side with crewed submarines – including the Astute-class hunter-killers and their successors – or independently.”

Known as Project Cetus, the vehicle, named after a mythological sea monster, is the latest in a growing list of investments by the British aimed at strengthening its ability to protect key underwater infrastructure from potential sabotage – a threat heightened by the recent attack on the Nord Stream gas pipelines in the Baltic Sea.

Last month the MoD revealed it was holding a competition, valued at around £20 million, to supply the Royal Fleet Auxiliary , the Navy’s support arm, with a remotely operated deep water salvage capability.

News of that development came just days after Defence Secretary Ben Wallace announced that leaders plan to accelerate the delivery of the first of two multirole ocean surveillance ships ordered by the British to protect underwater cables.

The first of the ships is expected to be handed over in the next few weeks, well ahead of the original delivery date.

In a statement announcing the unmanned submarine deal Wallace said that in order to meet the “growing threats to our underwater infrastructure, the Royal Navy needs to be ahead of the competition with cutting-edge capabilities. Project Cetus, alongside bringing forward the MROS ships, will help ensure we have the right equipment to protect the security of the UK and our allies.”

The bespoke unmanned vessel ordered by the British is the length of a London double decker bus, has a diameter of 2.2 meters and weighs 17 tons.

The British have already put money into a dedicated tech trials ship, and the MoD said Cetus is considered the “equivalent for sub-sea experimentation.”

The battery-powered vessel will be able to cover up to 1,000 miles in a single mission, though the range could be increased with the installation of additional batteries, said the MoD.

Other enhancements to the modular-built vessel could include an optional section that can be added to double its capacity.

Up to now the Navy has experimented with, and some imes operated, autonomous underwater systems in places like Scotland, where Britain bases its nuclear submarine flee.

Most, though, are small, off-the-shelf systems largely used in mine hunting.

First Sea Lord Adm. Sir Ben Key said the deal was a hugely exciting moment and in a different league to unmanned underwater vehicles purchased to date by the British.

“This extra large autonomous underwater vehicle is a capability step-change in our mission to dominate the underwater battle space, he said.”

Andrew Chuter is the United Kingdom correspondent for Defense News.

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