For better or for worse, humans have been training dolphins as soldiers of war since at least the 1960s; even to this day, the Russian government in particular has been known to enlist them in subterfuge.
But twenty years ago, the cash-strapped and crumbling Soviet Union sold a group of highly-trained aquatic assets to the Iranian government. Military.com (a subsidiary of Monster, apparently) has a good breakdown of the history, pulling largely from a BBC article published in 2000:
In 1991, after the fall of the Soviet Union, the dolphin unit was sent to the Crimean Peninsula from a base in the Russian Pacific area. There, the dolphins were trained to kill enemy frogmen using harpoons mounted on their backs. They would also swim at enemy ships in suicide attacks while carrying explosive sea mines, as they were able to distinguish between Russian and American submarines by the sounds their propulsion systems make underwater.
The highly trained killer dolphins were moved from the Black Sea to the Persian Gulf after Iran purchased them -- for reasons unknown. According to the Russian newspaper, Zhurid's work, which supposedly continued in Iran after the 2000 sale, was solely of a military nature.
It's a weird little factoid of military history. But here's the catch: dolphins can live for around 50 years. Which means that some of these dolphins could still be alive today. Which means it's not not impossible that a pod of these haggard soldiers is hanging around the coastal US, waiting for their retaliatory strike — though whether that would be against the country's foreign policy, or its oversights in regards to noise pollution from seismic testing, that's still up in the air.
For what it's worth, most war dolphins aren't actually trained to kill. But they are smart as hell, and do get high on pufferfish. Although it's still pretty messed to have sex with them, even if they are potentially capable of the cognitive processes require for consent. Clear communication is key here, folks.
Image via Wikimedia Commons