In March, British Prime Minister Keir Starmer said the country’s military could now board cargo ships that are under sanctions while traveling through UK waters. That announcement came as the government stepped up enforcement against Russia’s so-called “shadow fleet”—hundreds of vessels that Moscow uses to evade Western oil price caps imposed after its 2022 invasion of Ukraine. In June, Royal Marine Commandos carried out the first such operation, intercepting a sanctioned tanker in the English Channel. Days later, a Russian frigate escorting shadow-fleet ships fired warning shots near a British yacht in international waters, an incident the UK called isolated. The policy matters because it directly targets a key Kremlin revenue stream.