A homemade submarine carrying more than five tons of cocaine was intercepted in the Pacific Ocean off the coast of South America, the US Coast Guard said.
The 12-metre vessel had previously been detected by maritime surveillance, according to a statement published on Tuesday.
The Coast Guard boarded the self-propelled submersible on Sep 1 in international waters with the aid of the Colombian navy, the statement added.
On board, the Coast Guard discovered about 5.4 tons of cocaine, with a market value of more than US$165 million.
Four suspected drug smugglers were arrested during the operation.
Along with planes and swift boats, South American drug cartels - particularly from Colombia - use somewhat rudimentary submarines to transport drugs to Mexico and on to the United States.
In July, the US Coast Guard announced the seizure of 13 tons of cocaine from multiple operations throughout Latin America.