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FLORIDA– Eleven U.S. military members were presumed dead Wednesday morning, according to a U.S. Defense official, after their Army Black Hawk helicopter crashed into water off the Florida Panhandle during a nighttime training mission.

The helicopter, carrying seven Marines and four aircrew members, was reported missing during foggy conditions at about 8:30 p.m. (9:30 p.m. ET) Tuesday, and searchers found debris around Okaloosa Island near Eglin Air Force Base at about 2 a.m. Wednesday, base spokesman Andy Bourland said.

“We have begun to see debris washing ashore on both the north and the south side of the sound,” Bourland told CNN’s “New Day” on Wednesday morning.

The aircraft went down somewhere east of the Navarre Bridge, which crosses the Santa Rosa Sound connecting mainland northern Florida and a barrier island. On the other side of that island is the Gulf of Mexico.

An intensive search was underway Wednesday morning involving the Air Force, Coast Guard and civilian agencies, according to Bourland.

“It is still very foggy outside, which is impacting search and rescue efforts,” Eglin spokeswoman Sara Vidoni said. “… But multiple agencies are on scene, including Coast Guard who have secured the waterways.”

Second Black Hawk involved in mission got back safely

No one is saying what caused the accident, with Vidoni indicating only that there’s no indication of anything suspicious.

There was heavy fog in the area when the aircraft went missing, though the Eglin spokesman said it’s too early to tell whether that had anything to do with the crash.

The UH-60 helicopter wasn’t alone in the training mission. A second Black Hawk — assigned to 1-244th Assault Helicopter Battalion based in Hammond, Louisiana — safely returned to the base, some 40 miles east of Pensacola.

The aircraft were both assigned to the Army National Guard out of Hammond and taking part in what the U.S. military called a “routine training mission involving the Marine Special Operations Regiment” out of Camp Lejeune, a U.S. Marine Corps training base in North Carolina.

“Whatever the trouble was with the one aircraft, it did not involve the second helicopter that was participating in the exercise,” Bourland said.

Seven Marines based out of Camp Lejeune

All seven Marines involved in the crash were based out of Camp Lejuene, an expansive North Carolina base that is home to seven major Marine commands, one Navy command and a total of about 170,000 active deputy, dependent, retired and civilian personnel.

The names of those aboard — both the Marines and the four aircrew members — weren’t immediately released.

Introduced into Army service in 1979, the UH-60 Black Hawk is the successor to the UH-1 Huey, the iconic military helicopter from the Vietnam War era.

The twin-engine Black Hawk has a maximum speed of 173 mph. Its crew consists of two pilots and two crew chiefs. The Army says a Black Hawk can lift an entire 11-man infantry squad and its equipment.

The service says the Black Hawk’s airframe “is designed to progressively crush on impact to protect the crew and passengers.”

The Black Hawk has been modified for use by other branches of the military. The Navy uses the SH-60, known as the Sea Hawk, the Air Force the MH-60 Pave Hawk and the Coast Guard the HH-60 Jayhawk.

By Greg Botelho, Jason Hanna and Brad Lendon