The 50-shot barrage that killed an unarmed bridegroom outside his bachelor party came without warning and was over in matter of seconds, the police shooters’ commander testified today.

Lieutenant Gary Napoli claimed that when he heard gunfire erupt outside a Queens strip club, he believed it was his undercover team that was under fire. He also testified that he never heard his men yell “Police!” “Stop!” or any other order, nor did he see them actually shoot because he was taking cover.

“When it ended, there was almost like an eerie silence,” Lieutenant Napoli said without emotion. “I yelled out, ‘Has anyone been hit?’ I heard voices saying, ‘We’re OK.'”

Lieutenant Napoli, 50, was the first police officer involved in the operation to testify at the trial of three undercover detectives in the shooting of Sean Bell on November 25, 2006 — the victim’s wedding day. Though not charged, prosecutors say the lieutenant helped author a “tale of carelessness verging on incompetence.”

Detectives Michael Oliver and Gescard Isnora face manslaughter charges while the third detective, Marc Cooper, is charged with reckless endangerment in the slaying of Bell and wounding of two friends.

On the night of the bachelor party, the undercover detectives were responding to complaints about prostitution at the Kalua Cabaret. They say they fired their guns into Bell’s car only after Detective Isnora identified himself as a police officer, and after the car nearly ran him over and smashed head-on into an undercover police van.

No weapon was found in the car, and a grand jury investigation resulted in criminal charges against three of the five shooters. At the defendants’ request, the case is being heard by a judge and not a jury.

Yesterday, two of Bell’s friends told the judge that as the party broke up, the guest of honor exchanged glares and insults with an unidentified man dressed in black and possibly armed. The stranger, they said, struck a menacing pose by putting his hand in one pocket.

The defense has said Detective Isnora witnessed the standoff and — convinced that Bell and two friends were going to his car to retrieve a weapon — followed them on foot as the police van and another unmarked vehicle carrying Lieutenant Napoli converged.

Lieutenant Napoli — a 24-year veteran with experience in hundreds of undercover operations — testified that in the moments before the shooting, he received two urgent cell phone calls from Detective Isnora, saying, “It’s getting hot. … I need you here in a minute.”

When the lieutenant arrived at the scene, he heard a collision, followed by gunfire. He said his first thought was that occupants of Bell’s car “were trying to get away from us and they were shooting at us.”

He described ducking down in his car and drawing his gun, then crawling out the door and hitting the ground until the block went silent. He later approached Bell’s car and, noticing movement inside, ordered one of the men to show his hands, he said.

After an ambulance was summoned, Lieutenant Napoli and the shaken detectives gathered in the middle of the street — a scene he described as “surreal.” He suggested they were still unsure what had happened.

“We were all in shock,” he said. “We thanked God that none of us were hit and we were going home. … We didn’t really discuss anything more than that.”