The Navy on Thursday released its investigation into the death of a SEAL candidate who died after completing the notoriously grueling "Hell Week" training in California, concluding the program had operated with a number problems.

The investigation into Seaman Kyle Mullen's death found that Basic Underwater Demolition/Sea, Air, and Land (BUD/S) was "operating with a previously unrecognized accumulation of risk across multiple systems," including a lack of medical oversight, the Navy said. 

Mullen collapsed and died in February 2022 at a San Diego area hospital after he and another SEAL trainee reported experiencing symptoms of an unknown illness.

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Regina and Kyle Mullen smiling for camera

Undated image shows Regina Mullen with her son, Kyle Mullen. (Facebook/Regina Mullen)

In October, the Navy announced that he died of from acute pneumonia with a contributing factor of an enlarged heart. It ruled that Mullen’s death was "in the line of duty, not due to his own misconduct."

Mullen's death highlighted the brutal training potential SEAL candidates go through, which involves basic underwater demolition along with survival and combat tactics. Candidates get very little sleep and are tested on their physical, mental and psychological skills. The attrition rate is 50% to 60%. 

"Hell Week" is a five-and-a-half day test and is considered one of the most grueling periods of SEAL training. 

At the time Mullen's cause of death was announced, a spokesperson for the Naval Special Warfare Command (NSWC) said administrative actions had been taken against a former commanding officer of the Basic Training Command, the commander of the Naval Special Warfare Command, and some senior medical staff.

Three Navy officers received administrative "non-punitive" letters as a result of Mullen’s death, The Associated Press reported. Navy Capt. Brian Drechsler, who was commander of the Naval Special Warfare Center, received a letter and was pulled out of the job this month. Capt. Brad Geary, commanding officer of Naval Special Warfare’s Basic Training Command, and an unnamed senior medical officer also got letters. The report never names the medical officer, but notes a number of concerns with his command.

SEALs in BUDS SEAL training

U.S. Navy SEAL candidates, participate in "surf immersion" during Basic Underwater Demolition/SEAL (BUD/S) training at the Naval Special Warfare (NSW) Center in Coronado, Calif., on May 4, 2020. (MC1 Anthony Walker/U.S. Navy via AP, File)

In a statement, Rear Adm. Peter Garvin, commander, Naval Education and Training Command, said the probe identifies risks that aggregated as the result of inadequate oversight, insufficient risk assessment, poor medical command and control, and undetected performance-enhancing drug use, which sailors have used to try and pass the SEAL qualification course.

"At its core, the investigation finds that relentless and continuous self-assessment and self-correction within all departments of NSWC’s BTC is required," he said. 

In response to Mullen's death, the Navy said several improvements to its training program have been implemented, including greater instructor oversight and training; more thorough medical screenings for cardiac conditions; updated medical policies and standard operating procedures; and a new expanded authority to test candidates for PEDs.

Mullen, of Manalapan Township, New Jersey, joined the Navy in March 2021, according to his Navy biography. He reported to SEAL training in Coronado in July of that year. 

Rear Adm. Keith Davids, commander, Naval Special Warfare Command, said the Navy has a duty to learn from Mullen's death and to make sure similar occurrences don't happen again. 

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"I wish to extend my sincere gratitude to the Naval Education and Training Command investigation team for their insightful recommendations," he said, adding that the Navy will honor Mullen's memory by "ensuring that the legacy of our fallen teammate guides us towards the best training program possible for our future Navy SEALs."

Mullen's mother, Regina Mullen, has called for command officers to be held accountable for her son's death. 

"It's torture, not training," she told the Patch in March. 

Fox News' Jennifer Griffin as well as The Associated Press contributed to this report.