SAN DIEGO - A US Coast Guard cutter carrying $1 billion worth of cocaine and heroin seized from narcotics smugglers at sea returned on Monday from a four-month mission off the Pacific Coast of Mexico, Central and South America.The 32 metric tons of cocaine and 2 tons of heroin were stacked on pallets at the bow of the new Coast Guard Cutter Stratton, the lead ship among three vessels that took part in its maiden operation from April through July.The contraband was seized during some 30 separate interdictions of drug-running vessels, including two submarines and dozens of small outboard-powered boats called pangas, the Coast Guard said."Every one of these bricks of cocaine was headed for the United States," Coast Guard Admiral Paul Zukunft told reporters, adding that the United States consumes about 420 metric tons of cocaine each year.The $1 billion worth of narcotics unloaded at the US Naval Base San Diego marked the largest haul from a single Coast Guard mission, he said.The 32 tons of pure uncut cocaine aboard the Stratton would have been enough to produce street sales of the drug roughly equivalent to 33 million "lines" for snorting, according to the US Drug Enforcement Administration.Zukunft said Coast Guard anti-smuggling operations have netted 59 tons of narcotics off the shores of Mexico and Central America during the past year, more than was seized during the three previous years combined.The Stratton is part of the Coast Guard's new National Security Cutter fleet. Each one carries helicopters and small fast boats that are launched when a suspected smuggling vessel is spotted, Commanding Officer Nathan Moore said.Captain Daniel Pickles said interdictions often become a race to board the drug-running vessels before the smugglers can dump their cargo overboard or scuttle their own vessels."It's common to find the narcotics bales have been weighted so they sink when they're thrown overboard," he said. "It's part of the cat-and-mouse game."Federal officials declined to identify the cartels suspected in the smuggling.The seized narcotics, labeled with evidence tags, were to be moved to a secret location where they eventually will be destroyed, the Coast Guard said.