Nineteen underwater drones, some of them from the UK, have been sent to the Gulf as part of a naval operation designed to deter mine-laying amid continuing tensions between the west and Iran over Tehran’s nuclear programme.

Up to 40 nations will take part in the three-week exercise starting next week, the biggest ever undertaken in the region. The US navyvice-admiral in overall charge of the exercise, John Miller, said it was not a provocative gesture towards Iran.

In an interview, Miller said the importance of the Gulf’s sea lanes to the global economy made it essential to deter states as well as terrorists from attempts to mine waters through which 20 per cent of the world’s oil supply travels each day.

“Mine counter-measure activity is an inherently defensive exercise, there cannot be a misinterpretation that it’s an offensive exercise in any way,” said Miller, head of the US 5th Fleet based in Bahrain.

“It assures [everyone] that if someone puts mines in the water that a large number of nations from across the globe will respond. So if you have nearly 40 nations that are willing to just practice, just imagine how many nations would participate if someone put mines in the water? If you are thinking about putting mines in the water you pay the price for it in terms of world opinion and in relatively rapid fashion those mines are going to be taken out of the water.

“Japan gets about 75pc of their oil from the Gulf, China gets about 70pc, so imagine the effect on China’s economy if oil stops suddenly stops flowing. The effect would be immediate. It is important to the whole world those water ways are free-flowing.”

Though some are shy of admitting it, most of the countries around the Gulf are sending ships or providing support for the exercise, and Miller said he expected the Iranian navy would be watching closely.

“We don’t invite them but we know they are going to come,” he said.

“This exercise takes place in international waters and they have the same rights as we do. The Gulf is a relatively constrained water space, they are there and we are there. Every day we talk to each other - not on a government level but on a bridge-to-bridge level. It is a professional relationship, we get an outlier from time to time but we can deal with that.”

He said the imperative was to ensure the navies “don’t miscalculate each others’ intentions and unnecessarily have a tactical accident that leads to strategic consequences”.

Miller said unmanned underwater vehicles (UUVs) provided by the US and the UK, including the Seafox, would be a critical part of the exercise and for future efforts to keep the sea lanes open around the Gulf, particularly the choke points of the Suez Canal, the Strait ofHormuz and the Strait of Bab el-Mandeb.

The mini-subs can hunt and destroy mines that are on the seabed or floating, and can stay in the water for much longer than divers.

“We really are in the midst of a revolution in mine counter-measure technology,” said Miller.

“More unmanned, more automated. I think that we will see over the next couple of years a much stronger unmanned presence. If you can imagine mid-May in the Gulf when temperatures already pressing 100 degrees and having people up on flight decks or on small craft, you can only work them so long.

“You can work a UUV for longer than that and you can turn it around more quickly, you don’t have to rest it, you download the data and off it goes again.”

UUVs were first deployed in the Gulf last year, and they now formed part of the US and Britain’s permanent presence in the region, he said.

“Last year we had about five hours of experience [on UUVs]. They were brand new to us. Now we have 500 hours. Last year the US sent eight counter-mine ships to the region, but based on what we learned about UUVs, we have sent two of them back to the US.

“That capability and capacity has been replaced by unmanned technologies, and I foresee more of that in the future. We are rapidly approaching a period where we take sailors out of the minefield, but we don’t take sailors out of the process. Data still needs to be evaluated, decisions still need to be made.”

Miller’s second-in-command is a Royal Navy officer, Commodore Simon Ancona, who will have direct command of 35 counter-mine and other warships during the exercise, as well as the UUVs and more than 100 divers.

Ancona, brother of the comedian Ronni Ancona, said the exercise would allow the navy to practise skills “that are among those that define its role ... to deal with threats to freedom of navigation at sea, wherever in the world they might occur”.

One country that is not contributing to the exercise is China, the only one of the five members of the UN security council to choose not to get involved.

By arrangement with the Guardian