A Navy ship named in honor of the victims and first responders of the 9/11 attack on the Pentagon joined the fleet Saturday, serving as a floating tribute to the people who died that day and an active warship that can transport Marines around the world.

The Navy commissioned the USS Arlington in front of about 5,000 people in its new home port of Naval Station Norfolk. The amphibious transport dock is one of three ships named after 9/11 crash sites.

Two hundred pounds of steel salvaged from the Pentagon's wreckage was forged into a pentagon to be put on a permanent display aboard the ship in a memorial room and smaller pieces of the Pentagon sit on the commanding officer's desk. The ship also has 184 gold stars throughout its passageways in honor of those who died when American Airlines Flight 77 crashed into the Pentagon on Sept. 11, 2011.

"We are not a memorial, we are a warship. But we carry the spirit of those 184 people that died that day. We know why we got our name," Cmdr. Darren Nelson, the ship's commanding officer, told reporters the day before the ship was commissioned. "We teach that to the crew. Every crew member that shows up on board this ship learns and understands that 184 people gave their life for us."

Among those attending the pierside ceremony were first responders and family members of those who died the day of the attack. Rosemary Dillard, whose husband, Eddie, was on the plane as it crashed into the Pentagon, said seeing the Arlington join the fleet gave her a sense of pride.

"I know my husband died, or was murdered, because of a tragic thing. And I know this is a warship, but it all meshes together," said Dillard, who lives in Bloomfield Hills, Mich. "So it's important to me to see that all of the victims of 9/11 are honored and the memory lives on, and that we as Americans continue to know that we need to have things to safeguard our freedom and safety."

For some of the Arlington's crew members, the attack on the Pentagon was also personal.

Seaman Edward Florentino's uncle died in the attack that day. He said he originally wanted to serve on an aircraft carrier or another ship, but once he learned why the Arlington got its name that he was glad the Navy put him on it to be an original crew member, also known as a plank owner.

"Starting out, I never even know they were building this ship. I never knew I'd be a part of something like this. And being that I'm a part of this ship now, and that I'm a plank owner of this ship, means a great deal to myself and my family," said Florentino, who is from Lake Ariel, Pa.

The Arlington is now the Navy's 283rd warship. It is capable of carrying a landing force of up to 800 Marines, as well as amphibious assault vehicles and aircraft.

Two previous ships have had the name Arlington. The first was a cargo ship in World War II. The second USS Arlington was a Vietnam War-era communications relay ship, which the Navy says assisted with communications during a June 1969 conference between U.S. President Richard Nixon and Republic of Vietnam President Nguyen Van Thieu.

In honor of the northern Virginia community, two of the ship's main passageways are marked with road signs from major Arlington thoroughfares: Arlington Boulevard and Columbia Pike.

The other amphibious transport docks named after 9/11 attack sites are the USS New York and the USS Somerset. The USS New York was built with steel from the World Trade Center and recently completed its first deployment. The USS Somerset is named for the Pennsylvania county where United Airlines Flight 93 crashed.

Its bow stem -- the first part of the ship to push through the water -- was made from 7.5 tons of steel melted down from the bucket of a huge coal-mining crane that stood near the crash site. It was there that miners hung a large American flag to serve as a landmark and to honor the dead.

It was christened in July and will join the fleet in 2014.

"The USS Arlington, New York and Somerset serve as a reminder to us of all that we lost on 9/11. More importantly, they stand as a clear and distinguishable message to those who oppose democracy. This ship and those of her class represent America's resolve," Gen. James Amos, the Marine Corps commandant, said in his keynote address at the commissioning.