The yard's mission changed from shipbuilding to designing and manufacturing weapons and ammunition. It was integral to Washington's defense during the Civil War.
Building 197 was constructed in 1939 and called the Gun Assembly Shop. In the bathroom, Alexis assembled his gun. Minutes later, he walked out of the restroom with his Remington 870 tactical shotgun.
Alexis had customized the gun. It had been sawed down on both ends, making it shorter and more maneuverable. He had etched "My ELF weapon" into the stock. More alarmingly, the phrase "Better off this way" was also carved into it.
He carried double-aught buckshot shells in the cargo pockets in his pants, each packed with about a dozen pellets and capable of causing tremendous damage.
Meanwhile, Denise Robinson, who works on the fourth floor of Building 197, was chatting with co-workers. The U.S. Navy Band, which is based at the yard, was playing outside on the courtyard.
Alexis fired his first shot.
It was 8:12 a.m. Weaver was at his desk, one cubicle away from the atrium. His co-worker chuckled when he said the commotion in the building sounded like someone "was skateboarding on the ceiling." Then came a loud "bang." He thought someone dropped a safe in the atrium.
After the second loud boom, Weaver knew he was under attack.
"We hear pop, pop sounds." Robinson said. "We really didn't know what was going on."
Confused and curious, Robinson stood up to see above her cubicle walls. She saw her supervisor and the gunman. In her boss' face, she saw fear. In Alexis' she saw "a cold stare."
Weaver saw that 50-year old Frank Kohler was hit. So was 73-year old John Roger Johnson.
Weaver stood up, too. He saw Alexis at the end of his row of cubicles. He pointed the gun at the row of cubicles diagonal from Weaver where a friend was sitting.
"The reason he did not see me because he was so intent on shooting her," Weaver said.
Weaver's friend "turned around while she was curled up and watched him shoot her," he said, calling her the "bravest" and "luckiest person on the face of the Earth."
'Unbelievable how many shots were going off'
The friend survived but she lost much of a finger on her right hand and the blast grazed her scalp.
"[B]its of her scalp are scattered all over her cubicle" Weaver said.
Weaver got under his desk and pulled a two-drawer filing cabinet in front of him to hide.
Alexis then walked through a corridor with copy machines on one side and kitchenettes on the other.
Weaver called 911 from his cell phone. He later said it "was unbelievable how many shots were going off" while he was on the phone.
Bertilla Lavern's supervisor, Andy Kelly, told her to get down and then pulled her into his cubicle and told her to get under the desk.
When Lavern and Kelly got out from under the desk, she found co-worker Vishnu Bhalchandra Pandit who sat "right across" from her.
He was shot in the temple, but his pulse was "strong."
"I felt him breathe," Lavern said, describing that moment as "awesome and phenomenal." She said "it's like he heard me calling to him, talking to him, praying over him, letting him know that we love him and we want him to stay with us."
Lavern and some security guards loaded Pandit to an evacuation chair and carried him downstairs.