The disappearance last year of a Pearl Harbor Navy SEAL who was spearfishing with other unit members on a training free dive off Kaena Point was accompanied by sweeping procedural and safety violations, according to the Navy’s investigative report.

The death of special operations Petty Officer 1st Class Matthew John Leathers, 33, was likely caused by drowning due to shallow-water blackout during the breath-hold dive training, the command investigation concluded. No scuba gear was used for the exercise.

Leathers, a member of SEAL Delivery Vehicle Team 1, was wearing an estimated 8- to 10-pound weight belt on the day of his disappearance, Feb. 19, 2013, according to the report.

He was likely negatively buoyant, which would have kept him under water after a blackout, the report said. His body was never found.

Leathers, of Woodland, Calif., joined the Navy in 1998 and had been part of the unit at the SEALs’ Pearl City Peninsula compound since 2004. Members of Seal Delivery Vehicle Team 1 go on missions using flooded submersibles launched from submarines.

Leathers was described as a "super-nice guy" who would give others the shirt off his back, according to friends and media reports. He was the father of three young children and had deployed to Iraq and Afghanistan.

ALTHOUGH the training "was to be a (scuba) diving evolution, it evolved into a breath-hold dive, and there were no indications that pre-/post-dive checklists, proper dive briefs, medical briefs, medevac plan, communications plan, roles and responsibilities requisite to a safe evolution, lost diver emergency, etc., were discussed in any detail," the report said.

No swim buddies were designated. Nor was a standby diver chosen.

Group members lost track of Leathers — the dive supervisor for the exercise — who jumped into the water last, and was spearfishing like the others.

One of the other swimmers "believes" he saw Leathers nearby on the ocean side of a dive supervisor boat, which is the last time anyone had sight of the SEAL, the report states.

"This is an unfortunate loss of life, and our condolences remain with SO1 Matthew Leathers’ family, friends and teammates," Naval Special Warfare said Friday in a statement. "The command investigation is thorough, and it highlights the corrective actions Naval Special Warfare has taken to prevent this type of incident from happening again."

Portions of the investigation were obtained by the Honolulu Star-Advertiser through a Freedom of Information Act request. Some passages and all names except Leathers’ were blacked out.

Spearfishing while on a training swim became a specific focus of attention.

In an April 2, 2013, letter, an unidentified commander said, "I am returning the investigation to you for further investigation into pertinent information, specifically including to what extent, and to what level of command, breath-hold dive spearfishing on command time and with command assets, was authorized at SEAL Delivery Vehicle Team 1."

The command endorsement of the investigation noted the recommendation that SDVT-1 conduct an "internal inquiry" regarding the use of spearguns during official command exercises.

"I do not concur with this recommendation," a commander wrote in the endorsement. "The use of spearguns and other personal or non-governmental-issue items on training missions shall be prohibited throughout NSWG-3," referring to Naval Special Warfare Group 3, the umbrella command.

The investigation endorsement said a NSWG-3 training standdown was ordered from March 18 through April 5, 2013, and a commander’s conference was scheduled in San Diego.

"In addition to the standdown, I have issued a letter of instruction to all commanders and officers-in-charge, directing specific actions to be taken by all, as we review and change how we conduct business," the unnamed commander said.

Like the investigating officer, the endorsing commander did not believe Leathers’ death was the result of willful neglect. His death was determined to be in the line of duty and "not due to his own misconduct."

AT THE TIME of the training dive, Leathers was leading petty officer with the team’s Alpha Platoon.

Many of his teammates, including his commanding officer, were of the opinion that Leathers was among the most experienced SEALs and SEAL Delivery Vehicle operators. He could free dive down to 100 feet and was in excellent physical condition, the report says.

Ten sailors left the Pearl City Peninsula at about 11:45 a.m. on the day of the incident. They had two rigid-hull inflatable boats, chase and dive supervisor boats, an emergency truck and a personal vehicle.

During the drive, Leathers mentioned the possibility of going to Kaena Point instead of Electric Beach, the two locations discussed for the training.

One of the sailors reported that the chosen dive spot at Kaena Point had 9- to 10-foot waves, so the boats moved southward to a calmer area and dropped anchor.

The free dive was planned from 2 until 4 p.m. All the SEALs had fins, snorkels, masks, dive knives and weight belts.

"Look out for sharks," Leathers is reported to have said.

Before entering the water, Leathers advised others to be careful what they shot at with their spearguns, which one participant characterized as the "safety brief."

The SEALs were free diving to at least 25 feet. By 4 p.m., as the dive wound down, it was determined Leathers was missing, and a search began.

Around 5:45 p.m. the Coast Guard was notified about a "lost diver," and within minutes the first helicopter was on scene.

The search grew to include other SEAL surface craft; a Coast Guard C-130 aircraft, cutter and buoy tender; the vessel C-Commando; Honolulu Fire Department helicopters and lifeguard Jet Skis and swimmers, the report says.

Underwater caves were searched, and the SEALs looked as far as the eastern Kauai shoreline — where drift models indicated Leathers could end up — with foot patrols and small craft.

The command investigation also concluded that:

» The SDVT-1 "evolution sheet" used that day did not contain the information and checks and balances necessary to properly schedule and ensure appropriate control measures were in place.

» The exercise as conducted by Alpha Platoon "departed from the planned evolution in almost every significant regard, with no notice provided to SDVT-1 command group leadership."

» Platoon members did not perceive breath-hold diving to be a "diving" operation, despite Navy diving manual regulations to the contrary.

» The platoon did not follow standard dive- or swim-safety protocols.

Platoon members did not perceive the use of spearguns on evolutions to be unusual, and used them without sufficient safety measures.

» On the day in question, there were "shortcomings of leadership on multiple levels within Alpha platoon."

» All that was ever found was Leathers’ speargun.

"The work conducted in Naval Special Warfare is inherently dangerous and safety should never be compromised," the command said.