QUEZON CITY: A ranking Philippine Navy (PN) official on Tuesday said the Russian diesel electric submarine was likely in the process of recharging its batteries or refueling when it was spotted in the West Philippine Sea last Nov. 28. In a press briefing in Camp Aguinaldo, Quezon City, PN spokesperson for the West Philippine Sea (WPS) Rear Adm. Roy Vincent Trinidad said this was possible as a rescue tug and support vessel was seen eight to 10 nautical miles away from the Russian submarine. According to Philippines News Agency, the attack submarine identified as "UFA 490", a part of the Improved Kilo II class diesel electric attack submarines produced by Russia, was spotted some 80 nautical miles west off Cape Calavite, Occidental Mindoro. Trinidad noted that the Russian submarine was detected by the Western Command using its intelligence, surveillance, and reconnaissance capabilities. As a result, maritime patrol aircraft and a frigate were dispatched for visual confirmation. The Russian vessel reportedly co mmunicated that it was en route from Kota Kinabalu, Malaysia, after an exercise with the Royal Malaysian Navy, heading towards Vladivostok, Russia. On Monday, the Armed Forces of the Philippines indicated that the Russian submarine was waiting for favorable weather conditions before proceeding to its base in Vladivostok, approximately 2,200 miles away. Trinidad elaborated that while submarines are equipped to travel both on the surface and submerged, the need for refueling or recharging batteries is consistent with the operations of diesel-electric submarines, suggesting that minor repairs might have also been a motive for the stop. Meanwhile, the PN official highlighted that this incident marks the first time a Russian submarine was detected within the Philippines' exclusive economic zone, prompting a level of alarm. The detection prompted the deployment of aircraft and the missile frigate BRP Jose Rizal (FF-150) for visual verification. Trinidad clarified that under the United Nations Convention on the La w of the Sea, submarines or ships do not require permission from the coastal state when transiting an EEZ. However, the presence of the submarine could also be interpreted as a signaling maneuver, though primarily it was likely for logistical purposes such as refueling or minor repairs.