Four people were killed when a military-contracted helicopter crashed at Kauai’s Pacific Missile Range Facility while offering retrieval support for a training operation.

The contractor that operates the chopper said all four onboard were civilian employees.

Brian Beattie, director of operations for Croman Corp., said the Sikorsky S-61N had just retrieved an object from the water and was trying to drop it on the ground when something went wrong. The company’s choppers are used to retrieve material used in open-ocean testing at the missile range.

A PMRF spokesperson said the crash happened about 10 a.m. Tuesday near the north side of the installation. The National Transportation Safety Board, the Federal Aviation Administration and officials from Croman, an Oregon-based contractor, are investigating. Officials from the helicopter’s maker also were set to respond.

Thick black smoke billowing from the crash site was visible from miles away.

“Something caused that helicopter to accelerate and go down. It tweaked to the right and then immediately went straight nose-down in an accelerated speed ― straight down with like one second. That was it,” witness Chris Turner said.

He added that the weather at the time was calm.

Online flight logs show the chopper left Barking Sands at the Kauai facility at 9:24 a.m. and was in the air for 55 minutes when it got into trouble, flying a total of 83 miles.

The military and helicopter company have not released the names of those who died.

The Pacific Missile Range Facility is described as the world’s largest “instrumented multi-environmental range capable of supported surface, subsurface, air and space operations simultaneously.”

Some 900 people work at the Navy facility, only about 100 of whom are active-duty sailors.

The last military helicopter crash in Hawaii happened in 2017, when a Black Hawk helicopter went down off Oahu’s North Shore during a routine training mission. Five soldiers were killed.