Anti-submarine aircraft were deployed to the coast of southern California on Monday night, fueling speculation that a Russian submarine was spotted in the area.
Reports of a foreign vessel in the area circulated on social media, as the military conducted unplanned exercises at the same time late on Monday night.
The patrol includes multiple low-flying aircraft including a Navy EP-3E Aries II, which is used for electronic surveillance, a Navy P-3C Orion, which is used for submarine spotting, and a Boeing P-8 Poseidon used for anti-submarine warfare.
Additionally, a Royal Canadian CP-140 Orion, also known for submarine spotting, joined the search.
Southern California is home to several naval installations.
The activity comes as the Navy deploys warships off the North Korean coast, and as Russia pushes back against the US missile strike against a Syrian air field on Thursday.
“From now on we will respond with force to any aggressor or any breach of red lines from whoever it is and America knows our ability to respond well,” Russia said in a joint statement with Iran, the latter of which has been aiding Syria in its fight against ISIS.
North Korean is said to possess around 70 submarines, with the majority consisting of Sang-O class subs the communist nation uses to spy on naval installations.