US has intercepted multiple ship loads of Iranian weapons to Houthis in Yemen

CNN:

American warships have intercepted five shipments of weaponry to the Houthis in Yemen from Iran in the past year and a half, according to US Vice Admiral Kevin Donegan, who is in charge of American naval operations in the Middle East.

The first intercepted shipment was in April 2015 and since then, American ships have intercepted an additional four shipments, Donegan said.

The shipments included thousands of AK-47 automatic rifles, as well as anti-tank missiles and sniper rifles.

The US Navy determined that the ships carrying the weapons came from Iran based on an examination of the GPS data on board the five vessels as well as from interrogations of their crews.
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There is some speculation that Iran is ordering the firing of these weapons on US forces.   I suspect they are firing own US ships precisely because of the intercepts of the weapons shipments.  The Houthis are trying to break the blockade.