The Indonesian Navy says it has formed a team to investigate the deaths of two sailors during an exercise on the submarine KRI Cakra on Saturday.

“We are still waiting for the result of the investigation to find out the cause of the accident,” Commodore Darwanto, the chief of staff of the Navy’s Eastern Fleet Command, said, after the funeral of one of the sailors, Lt. Col. Eko Idang Prabowo, at Juanda Navy Cemetery in Sidoarjo, East Java, on Sunday.

Idang and Col. Jeffrey S Stanley died during an exercise while the submarine was at sea off the coast of Pasir Putih near Situbondo, East Java.

It was the first at-sea exercise held by the Eastern Fleet in escape, search and rescue techniques for submarine crews in emergency situations.

Eastern Fleet commander Rear Adm. Agung Pramono visited the sailors prior to the exercise. The entire crew of the KRI Cakra, including Idang and Jeffry, had completed confined-space evacuation exercises at the Eastern Fleet’s Underwater Rescue Agency.

The KRI Cakra’s captain, Lt. Col. Indra Agus Wijaya, said that the submarine had descended to a depth of 20 meters as part of the drill, where three teams of two sailors each were to don special diving suits, exit the boat and attempt to ascend to the surface.

“There was no problem with the first team, as they could get out of the submarine, but the second team was in trouble and the two officers died,” Indra added.

The sailors fainted after their ascent. They were placed into decompression chambers and given emergency treatment for nitrogen intoxication and severe decompression, two common problems facing divers, before their deaths, according to reports.

The third 2-man team did not ascend.

“On behalf of the Navy, we express our deepest sympathy on the loss of our two officers, who died in the line of duty,” Darwanto said.

Idang is survived by his wife, Dina Anggraini, 33, and his daughter Rara Chaira, 7, and son, Aditya Mardamar, 2, Antara reported. No information was immediately available on Jeffrey’s family.