Colombian marines discovered two homemade submarines that were to ship drugs from the country's Pacific Coast.
The two submarines, made of fiberglass, were found in a clandestine shipyard in the swamps around Colombia's largest port, Buenaventura, the navy said in a statement.
One of the vessels was ready for sea and the other was 70 percent completed when discovered.
Marines destroyed the unfinished submarine and sent the other, a 17-meter-long (56-foot-long) craft with the capacity to transport 5 tons, to a nearby naval base.
The navy said the two submarines belonged to Colombia's largest rebel group, the Revolutionary Armed Forces of Colombia.
In August, authorities discovered a makeshift submarine 20 meters (66 feet) long and 5 meters (16 feet) wide, hidden among trees on the country's Caribbean coastline.
Since 2005, the Colombian armed forces have uncovered nine home-built submarines.
The choice of the city of Helsinki is not incidental as the capital of Finland had hosted US-Soviet negotiations on the limitation of nuclear stockpiles in 1969