Sound Waves Help Scientists Find Dangerous Unexploded Bombs on Ocean Floor

Hundreds of underwater sites across America hide a dangerous secret beneath their seemingly calm surfaces: unexploded bombs and other military ordnance that never detonated as intended. These silent threats pose significant risks to human safety, especially as former military testing grounds transition to public use. Now, researchers are using advanced acoustic technology to locate these deteriorating weapons before they can harm anyone.

At the joint 188th Meeting of the Acoustical Society of America and 25th International Congress on Acoustics in New Orleans this week, scientists presented new findings on how sound waves can detect corroded munitions that visual methods might miss. The research could revolutionize how we find and safely remove these hazardous leftovers from military activities.

More than 400 underwater locations across the United States potentially contain unexploded ordnance (UXO), many in shallow waters where people swim, boat, and dive. After decades underwater, these weapons become nearly unrecognizable as they corrode and become covered with marine life.

The Challenge of Finding Degraded Weapons

“Many of these sites are in shallow water, potentially posing a threat to human safety, and date back several decades,” said Connor Hodges, a doctoral student at the University of Texas at Austin leading the research. “This long exposure to the environment leads to corrosion as well as encrustation in the form of barnacles or algal growth.”

This transformation makes standard sonar detection extremely difficult. As weapons rust and become covered with marine organisms, they blend into the underwater environment and no longer resemble their original shapes in sonar images.

Hodges and his team studied practice bombs recovered from Martha’s Vineyard that had been submerged for approximately 80 years. They compared these heavily corroded weapons with pristine versions to understand how their acoustic signatures change over time.

How Sound “Sees” What Eyes Cannot

What makes acoustic detection particularly valuable is its ability to penetrate surfaces and reveal what lies beneath them. Unlike visual methods that only show external appearances, sound waves interact with an object’s internal structure.

“Acoustic scattering techniques give an insight into the internal structure of the object imaged, as well as a method to ‘see’ into the seafloor,” Hodges explained. This capability proves crucial when munitions become buried under sediment or heavily disguised by marine growth.

The research revealed several key findings about how corrosion affects acoustic detection:

• Corroded munitions produce weaker acoustic signals than intact ones
• The resonance patterns change significantly as the metal deteriorates
• Size and shape alterations from corrosion create different acoustic signatures
• These changes can cause detection systems to miss or misclassify dangerous objects

Public Safety Concerns Drive Research

The research takes on new urgency as former military testing sites transition to public recreational areas. As waterfront property becomes increasingly valuable, more people may unknowingly encounter these dangerous relics.

“There is a risk of detonation if they are stepped on or otherwise disturbed,” Hodges warned. “This poses a larger risk to human safety in shallow waters, and UXO identification and recovery becomes vital as old sites are transitioned away from military use.”

How dangerous are these underwater munitions? While many practice bombs contain smaller explosive charges than combat versions, they still pose significant risks. Some may also contain toxic materials that can leak into surrounding waters as they degrade.

Future Directions for Safety

The research team tested AN-Mk 23 practice bombs—miniature bombs originally used for dive-bombing practice—recovered from a brackish pond on Martha’s Vineyard. These weapons had been submerged for approximately eight decades, providing excellent examples of long-term corrosion effects.

Looking ahead, Hodges plans to expand the research to include different types of munitions and various corrosion patterns. This expanded dataset will help create more accurate detection systems that can find even heavily deteriorated weapons.

“Underwater UXO can be tricky to find and recover, so it is important that this can be done safely and effectively,” said Hodges. “We hope this work will ultimately help save lives.”

Beyond the safety implications, acoustic detection offers practical advantages over alternative methods. “Using sonar to map the seafloor and detect munitions is also faster and cheaper than other techniques,” Hodges noted.

As former military sites continue to be repurposed for public use, this research represents a vital step toward ensuring these waters are truly safe for recreation. By understanding how time transforms these dangerous objects, scientists can develop better tools to find and remove them before they harm unsuspecting visitors—proving that sometimes, the best way to see danger is to listen for it.