Underlining its gratitude for China’s economic and military support for its war on Ukraine, Russia is again improving the People’s Liberation Army’s ability to hunt and sink U.S. Navy submarines.

From Monday to Wednesday, two Russian corvettes (the Gromkiy and the Rezkiy) will conduct exercises alongside the PLA Navy. The Russian defense ministry says the exercises will focus on “joint air defense exercises” and “an anti-submarine exercise with the involvement of the PLA naval anti-submarine aviation [forces].” The exercises will be held out of the southern Chinese port of Zhanjiang, close to the PLA’s main submarine force bastions on Hainan Island. In total, there are at least four major PLA submarine bases on or proximate to Hainan Island.