The haul is expected to deal a major blow to the funding of terrorism, which is known to generate cash through black market activities.
HMS Monmouth, nicknamed the Black Duke after James Scott, 1st Duke of Monmouth, is the seventh Royal Navy ship to bear the name, and was launched in 1991.
It is currently patrolling the Indian Ocean as part of an international coalition called Combined Task Force 150, which is seeking to “promote maritime security in order to counter terrorist acts and related illegal activities, which terrorists use to fund or conceal their movements”.
Sailors and Royal Marines from the Type 23 frigate destroyed 455kg of cannabis and 266kg of heroin after finding it hidden beneath three tonnes of ice in the freezer of a fishing boat.
The suspicious dhow – a type of vessel common to the Middle East and Indian Ocean – had been spotted by HMS Monmouth in an area which was not normally known for fishing.
Launching into action before the smugglers could destroy any evidence, HMS Monmouth sent two boarding teams in fast rigid inflatable boats to intercept the criminals’ vessel.
The teams spent 60 hours painstakingly scouring the vessel for narcotics, before eventually finding them hidden in a freezer beneath three tonnes of ice.
The haul means that Combined Task Force 150, which is currently being led by the French Navy, has now scored three major drugs busts in this month alone.
Earlier in May, Australian frigate HMAS Arunta pounced on a dhow and recovered 250kg of heroin.
That drug bust came hot on the heels of a double seizure of heroin by the French frigate Surcouf which brought in 400kg of heroin, worth around £120m on the streets.
Commander Ian Feasey, HMS Monmouth’s commanding officer, said: “Such a substantial seizure of drugs will deal a significant blow to the international narcotics trade which is known to provide funding for terrorist organisations.
“I am extremely proud of the professionalism, diligence and perseverance of my boarding team to achieve a result in such arduous conditions.
“This has been an effort by the whole ship’s company and their efforts speak volumes about the Royal Navy’s ability and commitment to preventing illegal activity on the high seas.”