New US sonar tech to hunt hidden WWII-era bombs buried at 400+ underwater sites
More than 400 underwater sites across the U.S. may be contaminated with unexploded ordnance (UXO)—decades-old bombs and munitions that failed to detonate and now pose serious safety risks, especially in shallow waters now transitioning to public use.
Connor Hodges, a Ph.D. student at the University of Texas at Austin, is working on advancing underwater detection by studying how UXOs degrade over time and how those changes affect their acoustic signatures.
'Many of these sites are in shallow water, potentially posing a threat to human safety, and date back several decades,' said Hodges. 'This long exposure to the environment leads to corrosion as well as encrustation in the form of barnacles or algal growth.'
UXOs may remain dormant for decades, but if disturbed—stepped on, struck, or moved—they could still detonate. Traditional sonar systems rely on recognizing shapes and materials underwater.
But as corroded bombs lose their distinct appearance, they begin to blend into the seabed. The acoustic signals they return weaken or shift, increasing the chance of false negatives during surveys.
To better understand how aged UXOs behave acoustically, Hodges and his team examined a series of AN-Mk 23 practice bombs—small-scale training bombs used during WWII. These particular munitions had been submerged in a brackish pond on Martha's Vineyard for over 80 years.
The researchers compared the sonar response of these corroded, biofouled bombs with that of pristine ones. They measured how sound waves scattered off the bombs from various angles and directions, discovering that degradation significantly changes the object's acoustic resonance and returns a much weaker signal.
'Acoustic scattering techniques give an insight into the internal structure of the object imaged, as well as a method to 'see' into the seafloor,' said Hodges.
As military sites are repurposed for civilian use, understanding how old munitions interact with sonar becomes increasingly vital. Hodges emphasizes the importance of UXO detection in environmental remediation and public safety:
'There is a risk of detonation if they are stepped on or otherwise disturbed,' he added. '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.'
Hodges plans to expand his work to include other types of munitions and explore different corrosion and encrustation scenarios. His research may ultimately contribute to more reliable models for sonar-based UXO detection—critical tools for military, environmental, and humanitarian operations.
'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.'
Hodges will discuss this research on Monday, May 19, at 8 am CT as part of the joint 188th Meeting of the Acoustical Society of America and 25th International Congress on Acoustics.
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