As the powerful motors of their speedboat roared, Spanish police used a thermal imaging camera to scan the sea in the Strait of Gibraltar for traffickers smuggling hashish from Morocco.
It's just after midnight and the cameras and radars that monitor the coast detect a dodgy looking boat.
The control centre informs police in Algeciras, a port city in southern Spain just 90 minutes by ferry from Morocco, and three officers immediately jump into the boat to investigate.
“They are likely looking for a place to unload their merchandise,” said one of them, Jesus, who declined to give his last name.
His colleague Claudio stood with one tense hand on the helm of the speedboat motored by twin 300 horse power engines and the other on the throttle.
The third officer manned an infrared camera.
The speedboat skimmed on the surface of the water between the lights of the port of Algeciras and those of the tiny British territory of Gibraltar, leaving a thick tail of foam.
“Aim the spotlight over there,” Jesus yelled out when they suddenly spotted an inflatable dinghy sailing without any lights.
The two occupants, who wore balaclavas and life jackets, did not resist as the police came on board.
But the officers found nothing. They then scanned the surface of the water with their spotlights and failed to find any bales. Police suspect they were smuggling tobacco which they threw overboard.
The two suspects were then on taken back to the port, their dinghy towed by the police.
But sometimes operations turn violent.
To smuggle hashish grown in Morocco's northern Riff mountains, traffickers use inflatable 8-12 metre long (26-39 feet) slender speedboats with up to five motors that can reach speeds of 60 knots or over 100 kilometres (60 miles) an hour.
Spanish police pursuing suspected smugglers in the area crossed into British waters and reached a Gibraltar beach earlier this month, prompting angry protests from London.
“These are risky situations, given the quick speeds and poor conditions of the sea” as well as the manoeuvres made by the smugglers to escape, said Antonio, another police officer.
Sometimes they try to ram the pursuing boat. Lately, they have developed a new tactic: they jump with their speedboat over the patrol boat to try and strike the police crew.
Smugglers have also been known to throw objects at the rotor blades of police helicopters. That caused a helicopter to crash a few years ago, killing a policeman, said Jesus.
Pilots employed by drug smuggling rings have also been drowned at sea, usually young men in their 20s who are drawn by a payments of several thousand euros in a region of Spain where the unemployment rate stands at around 40 percent, he added.
Big trafficking organisations employ up to 50 people — pilots, porters, drivers, lookouts — to receive shipments of one or two tonnes in bundles of 30 kilos, said Pablo Cobo, who is in charge of the local police unit against organised crime and drug trafficking.
Each kilo of hashish has a street value of 1,600 euros ($1,800) in Spain, he added.
Morocco has become the world's top producer and exporter of hashish over the past decades, according to a report from the Lisbon based European Monitoring Centre for Drugs and Drug Addiction.
Just 14 kilometres separates northern Morocco from Spain's southern Andalucia region, making it the ideal transit route for smugglers.
Of the 319 tonnes of hashish seized in Spain in 2013, 262 tonnes were found in Andalucia.
Spain accounted for nearly three fourths, or 73.7 percent, of the total amount of hashish seized in Europe in 2012, in the latest figures available from the interior ministry.
Traffickers monitor the movements of police patrols in a game of cat-and-mouse in the Strait of Gibraltar, sometimes sending out “dummy” speedboats without anything on board.
During the warm summer months when the sea is calm, traffickers use water scooters, which are smaller and harder to detect, to cross over into Spain with hashish — and illegal migrants.
“A water scooter can transport four bales of cannabis and two migrants,” said Jesus.
“When they arrive on land, it is up to them to take the merchandise to the buyer, as a way of paying their passage,” he added.