[Alex Lockie](http://www.businessinsider.com/author/alex-lockie) [Business Insider](http://www.businessinsider.com/russia-navy-frigates-mediterranean-threatening-us-strike-2018-3)
- Russia was seen sending anti-submarine warfare ships to the Mediterranean after threatening to retaliate against a hypothetical US strike on Syria's Assad regime.
- The US struck Syria, Russia's ally, in April 2017 using Navy destroyers. It could make sense for the US to send a submarine to attempt another strike in the future.
- Tensions between Russia and the US have reached a fever pitch after the UK accused Russia of carrying out a chemical weapons attack on its soil.
The US and Russia have become engaged in an increasingly hot war of words over the warfare and suffering in Syria, and Russia was seen sending heavy naval firepower to the region around the same time it threatened to retaliate to any US strikes.
Russia has supported Syrian President Bashar Assad for years during his country's seven-year-long civil war. Russia provides military support and airpower to help Assad cling to power as he fights off Islamist insurgents and a popular uprising in a war where his forces have reportedly killed the wide majority of the half million now dead.
Russia agreed to remove Syria's stockpile of chemical weapons in 2013, but international inspectors concluded in 2017 that Syria had used sophisticated chemical weapons in a massive attack on civilians.
The US responded with a naval strike that destroyed much of the airbase the Pentagon alleges carried out the attack. The next day, Russia vowed to retaliate if the US struck Syria, by destroying any missiles or launchers used.
After verbally sparring with Russia at the UN, the US on Monday said in no uncertain terms that if Russia could not hold to the UN-backed ceasefire, as multiple reports indicate it had not, the US would strike Syria again.
On both Tuesday and Wednesday, Devrim Yaylali, the man behind TurkishNavy.net and the popular Bosphorus Naval News, spotted Russian navy frigates transiting the Bosphorus Strait into the Mediterranean.
The frigates specialize in anti-submarine warfare, according to Yaylali, who told Business Insider that the deployments may or may not be routine, as sometimes Russian ships continue on past the Suez canal.
But tensions between Russia and the West are peaking after Russia's threats to fight back against the US in Syria and the UK accused the Russian state of carrying out a nerve agent attack on a former spy in the British countryside.
When the US attacked Syria as punishment for the chemical weapons attack in April 2017, it did so with Navy destroyers firing 59 cruise missiles.
The US also has submarines that can mount a similar attack, and if the US wanted to repeat the assault, it may be wiser to send a submerged vessel. A submarine would likely not create the obvious red flag of US destroyers returning to the shores where they once laid waste to a significant portion of Assad's air force.
Additionally, it's standard practice for any military to move supporting platforms into an area where it bases troops, so Russia's introduction of naval power into the Mediterranean may be simple protocol for protecting Russian servicemen in Syria.