The U.S. Navy has ordered an independent investigation into the Navy SEAL selection course following the death of a sailor during the program, according to a report from The New York Times.

Vice Chief of Naval Operations Admiral William K. Lescher called for the investigation in a letter obtained by the paper.

The investigation will focus on the Basic Underwater Demolition/SEALS (BUD/S) course, probing its safety measures and drug testing protocol as well as the qualifications of medical personnel assigned to the program.

Many sailors have been found to use performance-enhancing drugs to get through BUD/S, particularly during what is known as “Hell Week,” the most intense part of the selection course where sailors experience dire physical conditions, according to the Times.

The Aug. 31 letter also ordered investigators to look into changes made since the passing of Kyle Mullen in February. Mullen was a Navy sailor who died after being sent to the hospital in San Diego shortly following Hell Week.

An anonymous Navy official told the Times that the Naval Special Warfare Command (NSWC), which houses the SEALs, had also been investigating Mullen’s death before their probe was brought to a halt.

Leaders found that the NSWC report placed too much responsibility on Mullen rather than highlighting the flaws of the SEAL training program, according to the official.

The letter indicates that the Special Warfare Command will refocus its investigation into whether Mullen died in the line of duty, but will leave other questions to the independent investigators.

“The Navy remains committed to transparency and ensuring the final reports are thorough, accurate, impartial, and that confidence and credibility are maintained throughout the entire process,” it told the Times.

The Hill has reached out to the Navy for further comment on the investigation.