Mr Bergman pointed out that so far, no drug submarines have been detected under the sea, but seizures of semi-submersibles have dropped dramatically in the past two years.
That could mean that traffickers have already made the switch to submarines - and that they are evading detection.
"For the analyst looking at emerging threats," Mr Bergman said, "when they see this precipitous drop in semi-submersibles and then the advent of these two submarines, there's a concern that's raised. What are we missing?"
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