A century after World War I ended, discarded munitions from that and other wars continue to make their way onto beaches around the country.
Items ranging from tiny fuses to full-scale mines are displaced by beach replenishment projects, sucked from the ocean floor and pumped ashore, or by strong storms that uncover them.
The most recent discovery came earlier this month when seven WWI rifle grenades were found on the beach in Mantoloking, New Jersey, which is undergoing a beach replenishment project to undo damage from Superstorm Sandy more than five years ago.
Many of the items were simply dumped overboard at the end of World Wars I and II; others remain from military drills or target practice. They've been discovered in at least 16 states from New Jersey to Hawaii.
"Surprisingly or not, this stuff continues to turn up," said Niall Slowey, an oceanography professor at Texas A&M University, who has studied the phenomenon extensively. "They disposed of millions of tons of this stuff."
No one knows how many pieces of munitions remain offshore, partly because the military's own records as to how much was disposed of aren't great. A Defense Department report to Congress in 2009 said more than half of sea disposals of munitions was done in the Atlantic Ocean; the Pacific got another 35 percent, and lesser amounts were dumped off Hawaii, Alaska, the Gulf of Mexico and the Caribbean. The material was dumped as near as 5 miles from shore, in water as shallow as 50 feet.
Slowey and a colleague released a 2012 study estimating there are millions of pounds of undersea bombs in the Gulf of Mexico alone.
Disposal of unneeded munitions at sea was commonly accepted practice until 1970.
"They thought it was beyond harm's reach," Slowey said. "People could not envision that there would be any interaction with material that deep on the ocean floor. But there is a lot more on the sea floor than anyone could have envisioned."
New Jersey has been home to some well-publicized discoveries, including more than 1,100 pieces of munitions pumped ashore during beach replenishment work on a mile and a half of sand in Surf City and Ship Bottom on Long Beach Island in 2007. The items, mostly fuses, prompted temporary bans on the use of metal detectors and the digging of holes in the sand more than a foot deep. It also created a cottage industry in T-shirts with slogans like "Our beaches will blow you away!" and "I got bombed on L.B.I.!"
Similar material surfaced on the Jersey shore towns of Loch Arbour, Allenhurst and Deal in 2016 as part of another post-Sandy beach restoration project.
In May 2008, a bomb squad from the Massachusetts State Police detonated several pieces of unexploded ordnance left over from World War II on Chappaquiddick, including practice bombs.
In June 2013, a beachgoer discovered a partially buried German mine in the surf about 10 feet from shore in Bay Head, New Jersey, on the same day that the Assateague Island National Seashore in Maryland did a controlled explosion of a World War II bomb that had washed ashore.
In July 2015, a photoflash bomb, designed to illuminate the night sky over WWII battlefields, was discovered on a beach near Tampa, Florida, where authorities blew it up on the sand.
Military and civilian experts say they don't know of anyone in the United States being injured by munitions found on a beach, but agree the potential for injury is real.
"The problem is you just don't know," said Master Sgt. Brad Kline, an explosives disposal expert at New Jersey's Joint Base McGuire-Dix-Lakehurst. "There could be explosive residue left behind. It's definitely not worth the risk" of handling it. Military personnel use explosives to blow up munitions that are discovered on the beach and brought to the base.
In Europe, there have been injuries and deaths from unexploded munitions, including the 2005 deaths of three Dutch fishermen whose nets brought a WWII bomb to the surface, and other fishermen burned by chemical weapons they unwittingly dredged up.