Some 45 bales of cocaine weighing 900kg were found
A warship on which Prince William is serving has seized cocaine valued at £40m, in the West Indies, the Ministry of Defence has said.
The prince is spending five weeks on board the frigate HMS Iron Duke as it patrols the North Atlantic.
The MoD said the drugs had been intercepted on a speedboat, in a joint operation with the US Coast Guard, north-east of Barbados on Saturday.
William was involved in planning and surveillance during the operation.
The prince, or Sub Lt Wales as he is known on board, was part of the Lynx helicopter crew that observed the drugs boat.
The ship's captain, Cdr Mark Newland, praised William's maturity and contribution during the seizure.
He said: "This is a young man who has three, four years of professional military experience behind him.
"He is someone who contributes at every level. He is a very professional military officer, and very astute. He acts as I would expect a young officer of his experience and maturity to act in this type of operation."
Cdr Newland said he had been told to expose the prince to every aspect of front-line operations on the ship.
William, who joined the crew on 24 June, has endured rough seas and stormy weather during his first week at sea.
The 50ft (15m) speedboat was thought to be heading for Europe or Africa when it was ordered to stop.
US Coast Guard officials on the frigate boarded the vessel and discovered 45 bales of cocaine weighing a total of 900kg (1,980lb).
The speedboat had been spotted by HMS Iron Duke's Lynx helicopter, and suspicions were raised because the small craft was so far out at sea.
The drugs were taken on board the frigate and five crew members were detained. After the operation, the speedboat sank.
Cdr Newland, added: "This is a fantastic start to HMS Iron Duke's North Atlantic deployment.
"To have had a direct impact on the flow of cocaine into Europe just four days after we arrived in theatre shows the benefit the Royal Navy can have in the area of maritime security and counter drug operations."
The principal role of HMS Iron Duke is to support British territories, Commonwealth countries and other allies in the North Atlantic, including disaster relief if a hurricane strikes.