The royal receives word on his "selfless effort" after the sinking of the Swanland

Russia has expressed its heartfelt thanks to Prince William for helping to rescue two shipwrecked sailors from the sunken Swanland vessel in the Irish Sea, as the search continued Monday for five shipmates who are still missing.

“We know that you took an active part in the rescue and the two seamen were saved thanks to your selfless effort under the bad weather conditions,” the Russian ambassador to the U.K., Alexander Yakovenko, wrote in a letter to the Duke of Cambridge posted on Russian Embassy’s website.

Get push notifications with news, features and more.

Yakovenko added: Let me express to you and your colleagues my deepest gratitude for saving the lives of the Russian citizens.”

William, 29, was a co-pilot in a four-man helicopter crew that responded to a mayday call early Sunday morning. His crew was the first to arrive at the scene, airlifting two Russians to safety and taking them to William’s base at RAF Valley on the island of Anglesey in Wales.

“It was very windy, with very heavy seas,” an RAF Valley source tells PEOPLE.