Satellite images appearing to show dolphin pens belonging to the Russian navy have sparked reports of militarised sea life being used to stifle Ukrainian operations.
The harbour of Sevastopol, looking out to the Black Sea, is hosting the mammals to deter underwater missions by detecting swimmers and mines, according to a US Naval Institute (USNI) news report.
The photos come from Maxar Technologies, which has provided imagery of the war since Russia's invasion of Ukraine began.
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The USNI report explained it was unclear whether Ukraine actually intends to sabotage the base, but explained how marine mammal programmes train animals to perform protection tasks.
"This could prevent Ukrainian special operations forces from infiltrating the harbour underwater to sabotage warships," it said.
The US has a Mark 7 Marine Mammal System, better known as a bottlenose dolphin, to detect sea mines.
Before Russia's invasion, Gervase Phillips, a lecturer in history, politics and philosophy at Manchester Metropolitan University, spoke to Forces News about the role of militarised animals.
"We have nothing like a dog's nose to smell explosives yet and nothing as good at finding things on the seabed as a dolphin or a sea lion," he said.
"There are all kinds of those military roles for which, unfortunately, we have no practical alternative."