Now, an investigation has uncovered new information about the Yantar and its secretive work.

The investigation has been carried out by the Financial Times and using radar by satellites from the European Space Agency, located what it believes was the spy vessel lingering over critical cables in the Irish Sea in November.

According to the newspaper, the vessel had been attempting to conceal its activities at the time.

Radar imagery of a vessel in the Irish Sea allegedly matched the dimensions of the Yantar and fitted in with knowledge of its journey.

It is said that while this does not provide definitive detection, when combined with signals from a tracking system, it appears the ship was stationary for a number of hours.

According to the FT, the small area it was in contained three major data cables linking Ireland with the UK. Ireland, which has a tiny military, is heavily reliant on the UK and US for its defence.

Sidharth Kaushal, a maritime security expert from the RUSI think tank, suggested Irish waters are “a blind spot in the defensive architecture around the UK”.

Analysis by the FT suggests the Yantar is ‘once again flexing its muscles’ after seemingly having its surveillance capabilities ‘held back’ following Russia’s full-scale invasion of Ukraine in February 2022. The Yantar also allegedly hovered over two undersea cables off the Norwegian coast.

Earlier this year, NATO launched a mission aimed at protecting key underwater infrastructure in the Baltic Sea after a series of incidents in which power cables, telecom links and gas pipelines were damaged — many of which were blamed on Russia.

A UK Ministry of Defence spokesperson told the FT it was “sharply focused” on the threat Russia poses to maritime security. “Alongside our NATO and Joint Expeditionary Force allies, we are strengthening our response to ensure that Russian ships cannot operate in secrecy near the UK or near NATO territory,” the spokesperson said.