The mood in the National Guard headquarters in Hammond was somber Wednesday after a helicopter with four Louisiana guardsmen and seven Marines went down over water off the coast of Florida on Tuesday night during a training exercise.

A Pentagon official says the 11 are presumed dead, and a spokesman from the Air Force Base where the helicopter launched has confirmed human remains and helicopter debris have washed ashore.

Inside the National Guard Readiness Center in Hammond on Wednesday, two soldiers — one misty-eyed — were seen hugging, and when authorities held a news conference, many troops in fatigues stood quietly in the back and listened.

“Today, as you can imagine, is a tough day for the Louisiana National Guard and the Marine Corps,” said Maj. Gen. Glenn Curtis, who is the adjutant general of the Louisiana National Guard.

Marine Gunnery Sgt. Joshua Higgins, a spokesman for the Marine Corps at Camp Lejeune, North Carolina, said the Marines were participating in “amphibious operations.” Such training, which he called “a very routine exercise” involves Marines repelling out of an aircraft and either swimming or boating back to shore. During Tuesday’s training, the guardsmen piloted the helicopters while the Marines were to drop into the water and make for shore.

The two National Guard Black Hawk helicopters launched into thick fog from Eglin Air Force Base on Tuesday evening. One turned back, apparently because of the weather and safely returned to the base outside Pensacola, Curtis said.

The other was reported missing around 8:30 p.m. Search teams first found debris around 2 a.m., the U.S. Coast Guard has said.

Higgins said the wreck did not appear to have had any effect on other Marine training exercises.

The military has not named the service members who are missing. Curtis described the four soldiers as married fathers with the 1-244th Assault Helicopter Battalion based in Hammond. The soldiers piloting each helicopter during the training exercise were instructor pilots, who have to complete requirements beyond that of a typical pilot so they can teach others. Curtis said the crew of the downed craft combined for “several thousand hours” flying Black Hawks.

The Marines were part of a “really small, tight-knit” unit that Higgins said he could not name because it would give away their identities.

Both branches said they were not releasing the service members’ names out of deference to their families.

Kim Urr, who lives and works at a campground near where the helicopter crashed, said she heard something strange around the time the aircraft was reported missing.

“It sounded like something metal either being hit or falling over; that’s what it sounded like. And there were two booms afterward, similar to what you hear with ordnance booms, but more muffled,” she said.

Wednesday, crews scoured an area of about 51 square miles in the Santa Rosa Sound, a narrow strip of water between the mainland and a barrier island located between Pensacola and Destin, Coast Guard Chief Petty Officer Bobby Nash said. The Coast Guard unit based in New Orleans is heading up the search. Thick fog continued to be a problem.

“Weather has definitely been a factor for us,” he said. “The best tool we have at hand is our eyes. … (Search crews) have been impacted due to fog.”

The Coast Guard had to wait until around 11 a.m. — 12 hours into the search — before it was safe to launch a helicopter to survey the area.

Wednesday afternoon, Curtis said the National Guard was still holding out hope that some of the service members would be found alive.

“Our priorities are search and rescue … and to take care of our families,” the Major General said.

When asked about the Pentagon official’s presumption that all 11 troops had died, he responded “I do not have that information.”

Nash said the Coast Guard is also remaining optimistic.

“We’re looking for as many survivors as we can find. … We are completely focused on bringing people home.”

Curtis said the Fort Rucker Safety Center in Alabama would investigate the cause of the crash. Higgins said the Marines had requested the Naval Safety Center to assist.

Both branches said the cause of the wreck had not been determined. The investigation could be a “lengthy process. Very lengthy,” said Louisiana National Guard Col. Pete Schneider. President Barack Obama said he’s confident the investigation into the wreck will be detailed and thorough.

The crew of the helicopter that returned to base will be interviewed by investigators, Schneider said, adding that the craft that went down was equipped with a black box device.

The colonel denied a request to interview other members of the helicopter crew’s battalion, saying they were all still grieving.

“It’s hard. It’s real hard,” Schneider said.

The 1-244th was created in 1987 and has about 300 soldiers from Louisiana. The battalion operates 15 Black Hawk helicopters, according to a news release issued by the National Guard Wednesday.

The unit deployed to Iraq in 2004 and 2005 and again in 2009 and 2010. In 2005, helicopter pilot Michelle “Laz” Murphy told The Advocate she flew the imprisoned Saddam Hussein to his first court appearance while serving in the 1-224th.

The unit has also plucked evacuees off rooftops during Hurricane Katrina and participated in emergency operations surrounding Hurricanes Rita and Isaac as well as the 2010 Deepwater Horizon oil spill, Curtis said.

“They saved thousands of lives,” he said of their work during Hurricane Katrina.

Because of their close local ties, Curtis said when the unit deploys “it is the entire community that leaves.”

He said Wednesday afternoon he was making plans to visit the families of the missing soldiers. Officers trained to provide counseling had already been sent to stay with their family members, Schneider said.

Obama and Gov. Bobby Jindal have both called Curtis and offered their support to the guardsmen and their families, the Major General said.

The Associated Press contributed to this report. Follow Steve Hardy on Twitter, @SteveRHardy.