Spanish police have seized 127kg of cocaine found in a storeroom of a navy training ship which they said was loaded during a stop in Colombia.
It follows the arrest of three sailors after the boat returned to Spain last month, the Civil Guard said.
Drug traffickers contracted the sailors to transport the drugs when it stopped in Cartegena de Indias, they added.
The drugs, seized on Saturday in Cadiz, south-western Spain, were hidden in the ship's reserve sails.
Police were alerted to the drugs after the US authorities arrested two Colombians suspected of obtaining 20kg of cocaine from the sailors during a visit to New York in May.
The vessel, named Juan Sebastian de Elcano, had just completed a six-month tour and covered 18,000 nautical miles when the cocaine was discovered.