In waters off the coast of the British Isles, a tanker carrying sanctioned Russian oil sails drifts slowly towards a fishing vessel. The two ships briefly cross paths, before away sailing away from each other once more.

To the naked eye, nothing has changed. But to authorities tracking international shipping, the vessels have switched identities. The tanker appears to be an innocent fishing vessel, and vice versa. 

These manoeuvres, known as “handshakes”, are among the methods being used by Russia’s “shadow fleet” tankers to disguise their locations and avoid seizure by the UK and European nations.

The aim is to manipulate automatic identification system (AIS) tracking, which sends live information on vessels’ identity, port of origin, position and course to maritime authorities – particularly when passing through geographical choke points like the English Channel, where shadow tankers are at the greatest risk of interception.

As The i Paper revealed in July, vessels carrying illicit Russian oil are already adding days to their voyages by sailing around the north of Scotland in an apparent reaction to Britain’s seizure of the oil tanker in the Channel in June. 

Gonzalo Saiz Erausquin, a research fellow at the Royal United Services Institute who has been tracking changing behaviour by the shadow fleet, said there is “an active campaign to disguise those transits and operations to just get away with it”.

“As the routing has been diverted away from the English Channel and over the northern coast of Scotland and west of Ireland, that area has also seen increased AIS manipulation,” Erausquin said. “It aims to disguise any transit that might be happening, to confuse the trackers.”

There are several different methods of manipulating AIS data, including the “handshakes” where vessels temporarily switch identity; tampering with transponders to show false locations; or simply switching them off to “go dark”.

Joshua Tallis, a programme director at the Center for Naval Analyses, told The i Paper that AIS was vulnerable to manipulation because it was designed as a safety tool decades ago, when the current activity of the Russian shadow fleet was not envisaged.

AIS transponders are now being exploited in a “cat and mouse game” between these tankers and international authorities, Tallis said. “The ultimate goal is avoiding a boarding by what Russia would regard as a hostile entity.”

AIS “handshakes” allow vessels to swap identification numbers, national flags and information on their ports of departure and arrival. 

“So the vessel that’s under sanction is now steaming with the clean vessel’s AIS number, and they’ll often reconverge at a later point to swap back,” Tallis added. “It’s a way of temporarily obscuring the identity of the sanctioned vessel.”

In order for handshakes to work, both vessels must agree to exchange their details, which suggests that a secondary fleet of Russian-directed fishing trawlers may be operating alongside the Kremlin’s shadow tankers.

But the chain of command behind these smaller vessels is unclear, even to law enforcement agencies.

The technique is “not foolproof”, according to Tallis, because in many cases the ships involved will be visibly different.

But the deception can be sufficient to withstand scrutiny from automated systems or a “first pass” observation of navigation information by authorities. 

“As long as you can pass muster from a distance, then it’s okay that you’re not a perfect visual match for that vessel,” Tallis added.

The shadow fleet began as a means of sanctions evasion following the 2022 full-scale invasion of Ukraine, when Russian crude oil was made less profitable by a price cap imposed by G7 countries.

But some tankers have also been used as a launchpad for Russian spy drones or to damage undersea cables. A vessel seized by France last year was found to have employees of a Russian private military company on board.

On 16 June, two days after Royal Marine Commandos seized the , Russian warship the – which has previously accompanied shadow fleet tankers – fired warning shots near the yacht of a retired British couple sailing in the Channel.

Researchers at Lloyd’s List Intelligence have recorded a “significant uptick” in AIS manipulation around the world, which they said was becoming a “daily operational hazard” thanks to Russia’s expansion of its shadow fleet.

In the Gulf of Oman, analysts found that Russian crude oil was being secretly transferred between sanctioned and non-sanctioned tankers to allow the product to arrive in destinations including India and China on “clean” ships.

In those cases, the tactic used was the spoofing of tracking data to simulate false voyages.

AIS manipulation is most likely to be used by vessels sailing under false flags, according to experts.

This is because they are vulnerable to seizures by the UK or other countries on the basis that they are stateless and can be boarded under United Nations regulations.

To avoid being declared stateless and avoid boarding operations, an increasing number of sanctioned tankers are formally registering as Russian vessels, or joining the registries of other countries who are willing to host them.

The Royal Navy says it has increased efforts to track the shadow fleet this year, using ships and helicopters to physically monitor vessels in and around British waters.

Last month, three warships were deployed to track two Russian Navy warships and two sanctioned cargo ships over three days as they sailed through the North Sea and English Channel.

A Ministry of Defence spokesperson said: “President Putin relies on his shadow fleet to fund his illegal war in Ukraine. Every day our Armed Forces are working alongside allies to track, challenge and deter Russian activity in and around UK waters.”

Additional reporting by Sanya Burgess