Large spectator crowds flocked to the West Side as 3,700 United States and Canadian sailors, Marines and Coast Guardsmen began the city's 29th Fleet Week.
The NYPD worked to secure the Hudson River with its Harbor Unit, scouring underwater before the ships arrived.
Checkpoints went up at dawn Wednesday, with explosive-detection dogs and officers in body armor carrying heavy weapons. Other officers took up positions along the West Side Highway for several blocks, north and south of Intrepid.
Security also was tight around the ships, as Coast Guard cutters escorted the fleet to create a security corridor along the river.
The Parade of Ships started around 8 a.m., as ships from the Navy, Marine Corps, Coast Guard and Canada came into the harbor. The parade included five U.S. Navy ships, four U.S. Naval Academy Yard Patrol boats, two U.S. Coast Guard cutters and one Royal Canadian Navy ship.
Ships will be open for public tours from 8 a.m. to 5 p.m. starting Thursday.
All visitors must go through a security check before boarding a ship. Visitors over 18 must have state or federal picture ID. Strollers are allowed on the piers but not on the ships.
The ships can be seen along the Hudson River from Battery Park to just south of the George Washington Bridge. The flagship, Kearsarge, rendered a seven-gun salute as the ship passed Fort Hamilton, which offered a 15-gun salute in return.