SUNSET PARK — A Bay Ridge man who was on the ill-fated N train when a gunman opened fire last Tuesday morning recalled the moments of terror he and other straphangers faced immediately after the attack.

“It was pure chaos. There were people running, people were dropping onto the platform,” said Connor Armstrong, a New York State Supreme court officer who works in lower Manhattan.

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Armstrong, 34, a parishioner at St. Anselm in Bay Ridge, had transferred from the R train to the N train at the 59th Street station and, as it turned out, was one subway car away from the gunman. When the train pulled into the 36th Street station, all hell broke loose, he said.

“They made an announcement saying that the train was out of commission due to a smoke condition and that everyone should go to the R train across the platform,” Armstrong said.

As Armstrong would soon discover, the incident was much more than a smoke condition. 

“I went to switch trains and I looked to my left down the  platform. ‘Smoke condition’ was an understatement,” he recalled.

What Armstrong came upon was the aftermath of a shooting by alleged perpetrator Frank James, who was also armed with smoke bombs. 

James was arrested on Wednesday, April 13, in the East Village after he called the NYPD’s Crime Stoppers hotline to turn himself in.

As the drama unfolded before him, Armstrong ran over to some of the injured victims to offer first aid. People “were pretty much giving first aid to everyone that was hurt. People were applying tourniquets,” he said.

He came to the aid of a young man who was bleeding profusely. “He was afraid of passing out, but he didn’t want to lay down because he didn’t want to pass out. So I was holding him up and we applied a tourniquet to his  leg,” Armstrong said.

He then decided to enter the car where the shooting took place. “I checked the train car to see if anyone else was in there. Maybe there was a secondary device, like another explosive that hadn’t gone off. I didn’t see anything besides people’s shoes and luggage that were left behind,” he explained.

Armstrong was able to get to work that morning, despite the attack. He walked at least two miles — where he got on a No. 4 train for the trip to lower Manhattan. Once he was at work, he called his parents to let them know he was OK.

James was arrested on Wednesday, April 13, in the East Village after he called the NYPD’s Crime Stoppers hotline to turn himself in. He was arraigned in Brooklyn Federal Court on Thursday, April 14 — two days after the mass shooting — on a charge of conducting a violent act on a mass transportation system. If convicted, he could face life in prison. U.S. Magistrate Judge Roanne Mann ordered him held without bail. The judge also ordered him to undergo a psychiatric evaluation.

Witnesses told police the shooter, wearing a gray sweatshirt and an orange vest similar to that worn by MTA construction workers, was aboard an N train at 8:24 a.m.  and put on a gas mask as the train was entering the 36th Street station. He set off a smoke bomb inside the subway car and then opened fire, getting off a total of 33 shots, police said.

None of the victims suffered life-threatening injuries, but the shooting unnerved New Yorkers who were already leery about increased crime on the city’s transit system.

James has a lengthy arrest record, according to NYPD Chief of Detectives James Essig, who told reporters the offenses included trespassing, larceny, possession of burglary tools and criminal sex acts. The arrests took place between 1992 and 2007.

The next day, Armstrong went to work — on the N train. Although the shooting was in the back of his mind, he tried to proceed as if it were any other Wednesday.

“I commuted on the same train at the same time. The commute was no different, but I noticed more people being aware of their surroundings,” he said.

Armstrong said he is concerned about rising crime in New York City.

“We have the best law enforcement in the world, but there has been a severe increase in crime, whether the stats reflect it or not,” he added.

Investigators have not established a motive for the shooting rampage.