As the U.S. ramps up attacks on alleged drug-trafficking boats, blowing up vessels and killing their crews, American allies across the Atlantic are waging their own at-sea fights with suspected narcotics smugglers.

“Europe is literally being flooded with cocaine,” Artur Vaz, Portugal’s narcotics police chief, told Fox News.

“Criminal organizations… acquire the drugs in Latin America, and then the price at which they place it in the markets… there’s a big profit margin here,” said Vaz, director of the National Unit for Combating Drug Trafficking at Portugal’s Judiciary Police.

The drugs come over in cargo ships, high-speed boats and, increasingly, low-budget, semi-submersible vessels known colloquially as “narco-subs.” These boats sail largely undetected with only the top of the craft visible — often painted, researchers say, in steely blues and grays to blend in with the stormy Atlantic waves and evade surveillance efforts.

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Portuguese authorities scored a notable capture this fall, intercepting a narco-sub in the mid-Atlantic with 1.7 metric tons of cocaine on board. But European authorities acknowledge that many others are making it past their defenses.

“The interdiction rates for these subs is between 10%, roughly, and maybe as low as 5%,” said Sam Woolston, a Honduras-based investigative journalist specializing in organized crime.

“Even if one or two get nabbed by the authorities, it’s not enough to dissuade them.”

European authorities mostly choose to intercept narco boats, stopping far short of the Trump administration’s policy of destroying them. Instead, the often low-rung crews are detained for interrogation, in the hope of shedding light on shady drug kingpins, gang operations and distribution networks.

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Officials tell Fox News, though, that they would like to do more.

“We must be more muscular — that is, with greater means and a greater capacity for intervention,” said Vaz. “But, of course, within the rule of law.”

As for the narco-subs, those vessels aren’t new, but they never used to cross oceans.

“It’s mind-boggling, the level of sophistication,” Derek Maltz, a former acting chief of the U.S. Drug Enforcement Administration, told Fox News.

“But it’s all about the money, and it’s all about the risk, and right now I don’t think these networks perceive Europe as a huge risk for them.”

Journalist Woolston says the transatlantic voyage is typically crewed by “desperate people,” given its perilous nature.

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“You’ll be locked up in a very small compartment for days, usually inhaling things like diesel fumes. There have been cases of narco submarines found with a crew of dead bodies.

“The kingpins would not get on these boats.”