The Haitian capital's damaged port started receiving ships on Friday, 10 days after a devastating earthquake.
"We are here for humanitarian efforts for the Haitian people... to make sure there is no looting or things like that," said Petty Officer Third Class William Arocho.
"We are going to be standing by the port. We are going to set up our camp here."
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The coast guard deployment is part of a much larger US military operation that has seen paratroopers from the 82nd airborne division secure the airport and part of downtown Port-au-Prince and marines deploy to coastal towns.
They will work alongside a smaller but more established United Nations peacekeeping force and a coalition on UN agencies and aid groups responding to the chaos left behind by a quake that killed more than 110,000 people and left at least 600,000 homeless.
The port, already run-down before the quake, is a key part in this plan, being the only facility capable of bringing in large scale food and water shipments aside from the already overstretched airport.
"The port is open today for business," said US Colonel Charles Heatherly, spokesman for the military's Joint Task Force Haiti.
According to another American official, 250 containers have already been offloaded at the port in the past two days.
A pair of aid ships from France and the Netherlands have also unloaded supplies on the unsteady pier, while around 10 more are anchored offshore.
But gaping cracks still slice through the pier where ships dock, and it wobbled during each of the terrifying aftershocks that on Thursday and Fridaysucceeded the original catastrophic7.0-magnitude tremor.
US military divers were due to start repairing the pier on Friday and work is expected to last at least several weeks.
