After the Navy completed a multi-million dollar renovation on the space, Navy Yard workers returned to building 197, where contractor Aaron Alexis went on a shooting rampage on Sept. 16, 2013. (Video: AP)

Hundreds of Navy Yard employees reclaimed Building 197 as their workplace Monday, returning for their first official day there since 12 colleagues were killed in a mass shooting 17 months ago.

They gathered under a gray sky outside the new main entrance to the renamed and renovated building, which houses the Naval Sea Systems Command (NAVSEA). They saluted as a Navy band played and a flag was raised. A cold rain fell as they prayed for their workplace, where contractor Aaron Alexis stalked cubicles, hallways and stairwells with a ­sawed-off Remington shotgun on Sept. 16, 2013.

“Seventeen months ago, we got knocked down, but we didn’t stay down,” Vice Adm. William Hilarides, who leads NAVSEA, told the crowd. “The only thing that got us through the tragedy of September 16 was staying together. Today’s about looking forward, but we will never forget those we lost. Getting to this day has not been easy, but we are back.”

They watched as the admiral’s wife, Beverly Hilarides, smashed a bottle of champagne against the brick of the building to christen it, as the Navy christens new ships.

Afterward, William Hilarides commanded workers to “break my flag.” Breaking a flag symbolizes that an admiral or the most senior person is in the building or onboard a ship.

Navy Yard building reopens

WASHINGTON, DC - JANUARY 29: Building 197 in the Navy Yard, site of a mass shooting 18 months ago, is due to reopen on January, 29, 2015 in Washington, DC. (Bill O'Leary/The Washington Post)

The crowd turned toward the river and waited as the admiral’s flag was raised. The admiral then picked up a brown cardboard box, turned and went inside. Hundreds of workers followed.

“It’s a little surreal,” said a 49-year-old engineer. “But it’s good to get back into the building. It’s haunting, a little, thinking of what happened here. But everything is new again.”

Bill Deligne, the executive director of NAVSEA, which designs, builds and maintains the U.S. fleet, said he knew some workers would feel anxious about the return.

“This is such a tremendous event for us,” Deligne said. “As it built up last week, as we started to pack, you get a nervous feeling. I know the workforce was feeling it. There will always be a nervous feeling when the last memory you have is of the events of September 16.”

Deligne said he was still encountering workers who had not been back in the building, despite tours offered by NAVSEA to help them adjust. He said he would ask them, “‘If you haven’t been back, you should ask yourself why you haven’t. Maybe you ought to talk to someone about that.”

The building smelled of fresh paint and new carpet, as 400 returning employees began unpacking and organizing their new cubicles — part of a $6.4 million renovation designed to erase the worst memories of Alexis, 34, who was killed the day of the rampage by police.

Some workers took time out to visit the remembrance area dedicated to the 12 people who died in the shooting: Richard “Mike” Ridgell, Michael Arnold, Martin Bodrog, Arthur Daniels Sr., Sylvia Frasier, Kathleen Nark Gaarde, John Roger Johnson, Mary Frances DeLorenzo Knight, Frank Kohler, Vishnu Pandit, Kenneth Bernard Proctor Sr. and Gerald Read.

The memorial occupies the old entry area, where Ridgell, a 52-year-old security guard, was killed. A waterfall trickled over the black granite remembrance wall, which features a lighted panel that reads, “We memorialize as heroes those we lost and pledge that their lives and deeds shine forever bright. It was a day when ordinary people became extraordinary heroes and showed that courage lies in us all, even in the face of tragedy. Thousands returned to work just days later as a family. They would not let fear keep them away. They had a fleet to put to sea. — Secretary of the Navy Ray Mabus.”

Twelve lighted boxes commemorate the 12 victims. Someone had left a bouquet of sunflowers, lying on gray pebbles at the base of the wall.

Several workers quietly took seats on four marble benches. The Navy provided comfort dogs — black Labs and golden retrievers — to help people grieve.

John Brooks, 43, a supervisory program analyst who knew some of the victims, called it “a fitting memorial for the individuals who lost their lives.”

He and the other 2,800 people who work for NAVSEA need closure, he said. “But at the same time, these people matter to us. People want to forget about what happened, but we don’t want to forget these people.”

Not far from the remembrance area, a woman in a blue winter coat walked by sobbing, as a man tried to console her.

Support teams, including chaplains and employee assistance personnel, have been created to help people “reinhabit” the building, Cmdr. Paul Anderson, a Navy chaplain, said in an interview last week.

But some workers are still so traumatized that they could not bring themselves to reenter. The Navy has accommodated their wishes by transferring them to other jobs in other buildings.

Dozens of others have retired rather than return. Rory O’Connor, a spokesman for NAVSEA, said that 132 employees retired between Sept. 15, 2013, and Dec. 31, 2014, but officials could not break out how many of those departures were prompted by the shooting. Some workers had been offered early retirements to help with budget cuts.

Plenty of people have been eager to reclaim their workplace. O’Connor said workers began arriving as early as 5 a.m. Monday.

“I think people are excited,” he said. “Returning to our work home is a big step forward. The building looks great. People are at their desks.” The initial 400 workers will be joined by hundreds of others over the next few weeks.

Capt. Edward “Chip” Zawislak, who was rescued with three co-workers from the roof of Building 197 the day of the shooting, was among those excited to return.

“You walk into the building, and it’s a shot of positive energy,” said Zawislak, who was honored for helping a co-worker, Jennifer Bennett, after she was shot and seriously wounded in a stairwell.

The overhaul of the building includes new offices, doors, windows, carpet and soothing paint colors. A new cafeteria and visitors’ center are located near a Starbucks kiosk. Soundproof glass walls enclose a former atrium to help reduce noise.

A task force of NAVSEA employees oversaw the renovation of the historic brick building, which had been used during World War II to assemble guns for battleships.

The building has been renamed in honor of Joshua Humphreys, who designed the first Navy frigates. Hilarides said a new name was an important reminder of NAVSEA’s resilience.

Joe Heim contributed to this story.