The annual U.S. Navy invasion known as Fleet Week opens here tomorrow with a flotilla of five American warships and three Canadian entries to add an international flavor to the 21st annual observance.

Some 3,000 sailors and Marines will disembark from the ships during the eight-day event that includes public tours and a variety of aerial and simulated combat technique demonstrations by Marine Corps units.

A decade ago, as many as a dozen ships from several nations took part in Fleet Week, but the size of the assemblage has diminished in recent years. The last time it included a full-size aircraft carrier was in 2005, when the U.S.S. John F. Kennedy made its final appearance before being retired.

New York City policy bars nuclear-powered craft from the harbor, effectively denying port calls by the Navy’s newer fleet carriers.

The Canadians restore a cachet absent in 2007, when a destroyer named for Britain’s World War II prime minister, the U.S.S. Winston S. Churchill, provided the nearest thing to a foreign flavor.

A Navy spokeswoman at Norfolk, Va., Beth Baker, said the number of ships taking part in Fleet Week this year was not affected by naval deployments to U.S. operations in Iraq and Afghanistan, but by a shortage of dock space.

A museum ship that traditionally serves as host for Fleet Week, World War II aircraft carrier U.S.S. Intrepid, is still undergoing a two-year overhaul at Staten Island, where it takes up one entire side of a pier normally used for Fleet Week, Ms. Baker said.

Three ships will be moored on the other side of the pier, she said. The others will be tied up at Pier 88 on Manhattan’s West Side.

The opening procession will be led by a 40,500-ton amphibious assault ship that carries both helicopters and surface boats, the U.S.S. Kearsarge. Others are the guided missile cruisers U.S.S Leyte Gulf and U.S.S. Monterey, and guided missile destroyers U.S.S. Nitze and U.S.S. The Sullivans.

Two Canadian frigates, H.M.C.S. Toronto and H.M.C.S. St. Johns, and an oiler, H.M.C.S. Preserver, and the U.S. Coast Guard cutter Ida Lewis round out the lineup.

The Sullivans, named for five Iowa brothers who perished together aboard a cruiser in World War II, was the target of a January 2000 attack by Al Qaeda terrorists in the harbor at Aden, Yemen, which failed when their explosives-laden boat sank.

Ten months later, on October 12, 2000, the same group launched a successful attack against its sister ship, U.S.S. Cole, killing 17 crew members. Two Yemeni men were indicted by the Justice Department in 2003 for their part in the attack.