The employees on the Navy Yard’s IT team had jokingly nicknamed themselves “the lemmings,” so routine was their work. They sat overlooking the parking garage on the fourth floor of a nondescript government office building, in a corner their bosses called the “Cube Farm.” Their space was like any modern American office space — an ordered succession of 8-by-8-foot squares, a sea of blue partitions so indistinguishable that some staff members had given up on providing directions to colleagues. “Get lost until you find us,” one handmade sign read.

The first employees arrived at the Cube Farm that Monday in ­mid-September just before 6 a.m. In came 73-year-old John Johnson, known as “J.J.,” suffering from the beginnings of a post-vacation cold; and Mary Knight carrying pictures from her daughter’s recent wedding in North Carolina to hang above her new desk; and John Weaver on his 51st birthday, darting between cubicles, hurrying to see a supervisor, checking his BlackBerry. “Urgent!” one of his messages read. Some of the Navy Yard’s internal Web pages had crashed because of an issue with an expired security certificate.

“We need to get this fixed,” Weaver replied, and another week in Building 197 began with the kind of emergency they had come to expect.

The IT team was a blend of active military, civilian employees and contractors — “government lifers,” their boss called them, because turnover on her staff of 130 was practically nonexistent. What others dismissed as boring, the IT staff embraced as hallmarks of stability: a government job blocks from the Capitol, with cake to celebrate staff birthdays every fifth Wednesday, Navy-colored office beads each Mardi Gras, and actual gold stars hung each month on the cubicles of employees who received the best customer feedback.

Now, in the last week of summer, their morning interactions unfolded in the same predictable rhythm. Weaver fixed the Web certificate problem and then walked by Johnson’s desk, pretending, as always, to poke him in the eye. Johnson called his wife to check in on her at exactly 7:30. “Love you, beautiful,” he said. Dottie Jograj, who had been on staff since the building opened, went to the lounge and brewed a pot of the organic Sumatra coffee she always bought, because her colleagues liked it best. Johnson smelled the coffee and came by Jograj’s desk, where they had a version of the same conversation they’d had every weekday for years.

“How’s my Dottie today?” he asked.

“I’m fine,” she said.

“Just fine?” he said. “Why not good?”

“Okay then. For you, I’m good.”

She had been working at the same cubicle for 11 years — “my living room,” she called it — and she had decorated her desk with the artifacts of her profession: an old wireless headset, antique cellphones and a first-edition BlackBerry. She had pictures of her grandchildren taken at the beach back home in Jamaica. She had leftover dishes from the feasts she sometimes hosted in her cubicle, cooking enough jerk chicken and peas to feed the half-dozen co-workers who crowded around her desk. “Ms. Dottie,” they called her, and she prided herself on being the matriarch of the “office family,” she said. A few weeks earlier, after a mouse had come running through the Cube Farm, she had helped affix warning signs to the bottom of every cubicle as a joke. The sign showed a gray mouse, circled in red and crossed out with a black dagger. “No intruders,” it read.

Jograj drank her coffee and watched the Cube Farm come alive. She loved that she could name the spouses of every person on the team. She loved the gentle pace of the place, the steady hours and the absolute predictability. “So comfortable,” she said. She watched Susan Becker walk into her small office down the hall and check the date on her calendar, retirement now only 47 days away. She watched a colleague to her right stand up for the bathroom and two more co-workers head downstairs for their usual morning tea.

It was 8:11 on another Monday morning — the beginning of a routine American workweek in the most routinely American place.

Twelve people, plus the shooter, were killed in the shooting rampage at the Washington Navy Yard.

Jograj was starting to type an e-mail to one of her colleagues when she heard two blasts, followed by what sounded like a shrill scream. She turned around from her desk, confused, half expecting to see a mouse.

“Oh dear God,” she said.

* * *

The gun, she would recall later, was less than 12 feet from her face.

It was double-barreled and at least two feet long — black and smoking and utterly unmistakable. But still, for a fraction of a second, Jograj could make no sense of what the thing was, or what was unfolding in front of her. Even in this building, where the Navy had once manufactured 16-inch guns for warships during World War II, her co-workers were preoccupied mostly with cybersecurity. No one had noticed a man with wide eyes, a short-sleeved blue shirt and an ID badge getting off the nearby elevator at 8:09 a.m. Nobody had paid attention to him as he entered the bathroom near the Cube Farm with a black bag and emerged with a gun six minutes later. Nobody had been given enough time to comprehend the two shots already fired at Frank Kohler in his office, immediately across the hall.

Even now, as Jograj stared at the shooter, she wondered: Had the two deafening sounds she had just heard been the popping of bubble wrap? Or chairs that crashed down onto the atrium floor? Who was this skinny man standing three cubicles away from her, looking so calm, holding this long weapon, now directing it over the lowest wall of a cubicle, now aiming it at Johnson, now tightening his jaw?

Wham. The explosion shook her desk.

“He has a gun!” Jograj screamed, everything suddenly clear.

Smoke and blood and plastic particles from the cubicle wall filled the space around her. She started to dive under her desk, expecting the gunman to aim at her next, but instead she saw him turn to look down the hall. Knight was walking toward them, seemingly unaware of what was unfolding. She had been so joyous lately, sometimes singing to herself: a recent, hard-earned promotion, a new job moonlighting as a community college professor, and a daughter just married — a new chapter of life beginning after 50.

Again the gunman aimed his weapon. Again Jograj heard a blast.

Four shots now in less than a minute. Three people were already dead.

Jograj hunched under her desk and told herself to keep quiet. She closed her eyes to pray and thought instead about Johnson. He had barely had time to look up at the gunman, never raising his eyes above the silly baseball bobble-head figure that sat on his desk. She remembered how he had lightly teased her months earlier for being squeamish. They both liked to fish, but she always made someone else bait her line and clean the catch. She hated the idea of the fish suffering. “Oh God,” she whispered now. “Oh God. Oh God. Oh God.”

In the next row of cubicles, Weaver heard the explosions and stood from his desk, lifting onto his toes for a better view over the five-foot-high cubicle walls. He saw the shooter steadying his rifle 10 feet away, aiming at a young woman who sat a few cubicles farther down the hall. The woman lifted her hands to her head to protect herself. Wham. The gun fired. The Cube Farm shook again. The shot hit the woman’s finger and grazed her head. Was she okay? Weaver didn’t know. He dived down and crawled under his desk, admonishing himself for standing up in the first place. “So stupid,” he later said. Had the shooter seen him? He grabbed a metal filing cabinet stuffed with old computer equipment and slid it under the desk for cover. Then he clutched his knees to his chest, held his breath and listened.

The explosions continued down the hall, three or four of them at a time. Weaver hugged his knees closer, a 6-foot hockey player trying to disappear into himself. Even more terrifying than the commotion were the moments of relative silence. First the clicking sound of a gun reloading. Then the steady footsteps of the shooter moving down the hall. Then the muffled whispers and whimpers all around him now.

At 8:17, when he guessed the shooter was too far away to hear him, Weaver reached for his work BlackBerry and dialed 911. It had been two minutes since the shooter first entered the Cube Farm. The operator asked for the address of the building. Weaver answered in a cautious whisper.

“1-3-3-3 Isaac Hull Avenue,” he said. He heard the operator typing. She couldn’t find the building on her computer. He waited for a few seconds and then repeated the address again.

“1-3-3-3 Isaac Hull,” he said, louder now. “Come on. Hurry!”

* * *

The fire alarm went off five minutes into the shooting, and Weaver resisted the temptation to cover his ears. The cacophony now was deafening and disorienting; a team of first responders began returning fire while two automated voices alternated over the loudspeaker, one male and one female: “There is a fire in the building. There is a fire in the building.”

“Run!” Weaver screamed, kicking the filing cabinet away from his desk and pushing his way out of the cubicle. He could hear shots coming from the other side of the fourth floor. They sounded like the same shotgun blasts he had heard earlier, and now they were coming closer. He guessed the sound was 70 yards away. Fifty yards. Forty. Could he beat the shooter to the stairwell? He sprinted down the hallway, crouching low, passing three bodies on his way, and finally pushing his way out the exit. He spotted the young co-worker he had watched get shot in the finger and neck a few minutes earlier. “What happened?” he asked. She held up her bloody finger and brushed the brown hair from the back of her neck, revealing a trail of buckshot. She had been partially scalped, but it was a surface wound, Weaver thought.

“You are the luckiest person in the world,” Weaver told her, guiding her down the stairs.

Back in the Cube Farm, Jograj stood up to run, too, but then another voice came over the intercom. This time it was not a recording. “Live shooter. Shelter in place,” the voice said. Jograj ducked under another desk where two colleagues were already hiding and knelt in between them.

In her office several yards down the hall, Becker, an IT supervisor, tried and failed to lock her door. She had spent 33 years working for the government, and she had filed paperwork to retire Nov. 1. She had bad knees and the beginnings of a flu, but she and three colleagues pushed chairs up against the door of her office, barricading themselves inside for what seemed like an hour. They thought they heard the gunman go downstairs to the third floor, down to the lobby and then back upstairs. They watched him reload in the hallway, his silhouette darkening the office door. They turned out the lights and listened in silence to the firefight. “People are dying out there,” Becker whispered at one point, hoping that acknowledging the reality might somehow minimize her fear.

Back under the desk in the Cube Farm, Jograj heard a thundering herd of footsteps coming closer a little after 9 a.m. It sounded more like a group than a lone shooter. Maybe, finally, here came help. She stuck out her hand. “Please,” she said. “We are over here.”

“How many?” a policeman responded.

“Three of us.”

Four policemen walked over to the desk and helped pull the IT workers out into the open. “Don’t look at what’s around you,” one of the officers cautioned, but Jograj looked anyway. The ordered rows of the Cube Farm had become a walkway of broken glass, shell casings and littered office paper. There were the members of her office family within view, so many dead: Frank, J.J., Mary, Sylvia and Gerry, plus seven more victims in other parts of the building that she didn’t yet know about. Her routine Monday morning in the most ordinary American space had become something else — something discordant and haunting and yet, in its own way, increasingly familiar, too.

She stayed with the bodies for a few seconds, not wanting to stare but also not wanting to leave them. A police officer reached for her arm.

“Twelve down,” she heard the policeman say into his radio, his voice flat, as she followed him out of the Cube Farm.

Julie Tate and Peter Hermann contributed to this report.