HAWTHORNE, Nev. (AP) — Hundreds of residents in a rural community steeped in military history turned out to mourn the loss of seven Marines as investigators arrived at an ammunition depot to try to determine how a mortar shell exploded at the Nevada base and sent shrapnel flying into troops during a training exercise.

Families with children clutching small American flags were among the nearly 300 people who attended the brief memorial service Tuesday, where a trumpeter played taps at a city park as a giant American flag flew at half-staff across the street from the base at dusk.

Marine officers from Camp Lejeune, N.C., who arrived at the Hawthorne Army Depot on Tuesday, could not attend the memorial, as they began the task of figuring out what caused a mortar shell to explode in its firing tube. The accident prompted the Pentagon to immediately halt the use of the weapons until an investigation can determine their safety, officials said.

The explosion Monday night at the sprawling facility during an exercise involved the 2nd Marine Expeditionary Force from Camp Lejeune. Seven men were killed and eight were injured, officials said.

Hawthorne has been an important installation in American military history since World War II, when it was the staging area for ammunition, bombs and rockets. The facility has downsized in recent years but still serves as a munitions repository and disposal site, along with being a training facility for troops as they take advantage of terrain and climate similar to places like Afghanistan. The facility is made up of hundreds of buildings spread over more than 230 square miles, and bunkers dot the sagebrush-covered hills visible from the highway.

Even though the Marines were from the other side of the country, locals still feel a strong sense of pride in the military because the town’s history is so deeply tied to the armed forces.

The town calls itself “America’s Patriotic Home” and is home to the Hawthorne Ordnance Museum, which displays hundreds of shells, munitions, battery guns and weapons dating to World War II. Red, white and blue sculptures made of former shells and bombs are on display in town. Storefronts carry names like Patriot’s Plaza. The sign on a business Thursday carried the message, “Please Pray For Our Marines.”

“The evening of March 18, 2013, will forever be remembered as a moment of profound tragedy in Mineral County,” District Attorney Sean Rowe told the memorial service. “You have given meaning to the phrase, ‘America’s Patriotic Home.'”

The identities of those killed aren’t expected to be released until 9:45 p.m. Eastern time, according to Cpl. Daniel Wulz, a Marine public affairs officer. The military is waiting until 24 hours after families are notified.

However, family members confirmed the names of two victims on Wednesday.

The grandfather of a 23-year-old Connecticut native confirmed his grandson had been killed. Roger Muchnick grew up in Westport, Conn., and had served in Afghanistan, according to Jerome Muchnick. The young man was considering going to college after serving in the Marines. The elder Muchnick said his grandson was a vibrant, loving man, and he’s devastated by his death.

Also among the victims was 21-year-old Marine Lance Cpl. Josh Taylor. Taylor had fulfilled a nearly lifelong dream when he joined the military right after graduating from a southeastern Ohio high school in 2010, according to his grandfather, Larry Stephens.

Stephens said his grandson had talked about being a Marine since he was about 5, watching the History Channel and studying the military. After joining, he worked with mortars and served tours in Afghanistan and Kuwait, and was preparing for another tour in Afghanistan.

Taylor was engaged to be married, with a wedding planned for May.

The impact of the accident was immediately felt.

The Pentagon expanded a temporary ban to prohibit the military from firing any 60 mm mortar rounds until the results of the investigation. The Marine Corps said Tuesday a “blanket suspension” of 60 mm mortars and associated firing tubes is in effect.

The Pentagon earlier had suspended use of all high-explosive and illumination mortar rounds that were in the same manufacturing lots as ones fired in Nevada.

The 60 mm mortar is a weapon that traditionally requires three to four Marines to operate, but it’s common during training for others to observe nearby.

The mortar has changed little since World War II and remains one of the simplest weapons to operate, which is why it is found at the lowest level of infantry units, said Joseph Trevithick, a mortar expert with Global Security.org.

“Basically, it’s still a pipe and it’s got a firing pin at the bottom,” Trevithick said. Still, a number of things could go wrong, such as a fuse malfunction, a problem with the barrel’s assembly, or a round prematurely detonating inside the tube, he said.

A Marine Corps official said an explosion at the point of firing in a training exercise could kill or maim anyone in or near the protective mortar pit and could concussively detonate any mortars stored nearby in a phenomenon known as “sympathetic detonation.” The official spoke on condition of anonymity because the individual wasn’t authorized to speak about an ongoing investigation.

The official said a worldwide moratorium after such an accident is not unusual and would persist until the investigation determines that the weapon did not malfunction in ways that would hurt other Marines or that mortar shells manufactured at the same time as the one involved in the accident were safe.

The investigation will focus on whether the Marines followed procedures to properly fire the weapon, or whether there was a malfunction in the firing device or in the explosive mortar shell itself, the official said.

Renown hospital emergency physician Dr. Michael Morkin said at a news conference that some of the injured Marines he treated were conscious and “knew something happened but didn’t know what.” Morkin said the Marines mostly suffered blunt force trauma from shrapnel.

“They’re injuries of varying severity … to varying parts of the body. They’re complicated injuries to deal with,” he said.

The Hawthorne depot opened in 1930, four years after a lightning-sparked explosion virtually destroyed the Lake Denmark Naval Ammunition depot in northern New Jersey, about 40 miles west of New York City. The blast and fires that raged for days heavily damaged the adjacent Picatinny Army Arsenal and surrounding communities, killing 21 people and seriously injuring more than 50 others.

Retired Nevada state archivist Guy Rocha, who initially said he was unaware of any previous catastrophic events at the Hawthorne depot since it opened in 1930, said Wednesday that more research turned up three other fatal explosions.

An Oct. 5, 1951 blast killed five people, another on Sept. 3, 1966, killed two men, and a rocket explosion on May 26, 1971, killed three, Rocha said.