Comment by _--__--__
"In addition to the participation of the Portuguese Navy and Judicial Police, the operation was supported by the United States Drug Enforcement Administration (DEA) and the Joint Inter-Agency Task Force – South (JIATF-S), and the United Kingdom’s National Crime Agency (NCA), working together within the scope of MAOC-N."
from the linked press release, I'm assuming DEA tipped off the Euro agencies that the sub was headed their way
It's equally, if not more, probable that the intelligence about shipment departures came from non-US MAOC-N members and the "the operation" of tracking the craft was where the US liasons provided assistance.
https://en.wikipedia.org/wiki/Maritime_Analysis_and_Operatio...
The US isn't the only country with agents blending in on the supply side keeping eyes and ears on activity.
The EU end has had repeated success infiltrating and cracking 'encrypted' criminal networks on the demand side of such markets.