A Russian Kilo-class attack submarine was detected transiting the West Philippine Sea for the first time on November 28, prompting concern from Philippine officials and military forces. 

West Philippine Sea is the official designation by the government of the Philippines to the parts of the South China Sea that are included in the country’s exclusive economic zone (EEZ).

President Ferdinand Marcos Jr described the development as “very concerning,” underscoring the heightened sensitivity of maritime activity in the region.

The Philippine Navy reported that the submarine was spotted on November 28, approximately 80 nautical miles west of Cape Calavite, Occidental Mindoro. It was navigating through the Philippines’ EEZ after completing joint military exercises with the Malaysian Navy in Kota Kinabalu.

“All of that is very concerning. Any intrusion into the West Philippine Sea, of our EEZ, of our baselines is very worrisome,” Marcos told reporters on December 2. While expressing his concern, he added: “We’ll let the military discuss it with you.”

The submarine, identified as a Russian Kilo-class vessel, is a diesel-electric attack model originally designed in the 1970s by the Soviet Union. Despite its age, the vessel remains a critical component of the Russian Navy, with upgrades leading to the Improved Kilo II (Project 636.3) variant, introduced between 2014 and 2016. 

These submarines, often referred to as the Black Hole by the U.S. Navy, are recognized for their stealth capabilities, advanced weaponry, and capacity for covert operations.

National Security Council’s spokesperson Jonathan Malaya confirmed that Philippine forces issued a radio challenge to the submarine after its detection, which was met with compliance. Rear Admiral Roy Vincent Trinidad, Navy’s spokesperson for the West Philippine Sea, emphasized the significance of the encounter.

“This is the first time we’ve detected, responded to, and tracked a Russian submarine,” Trinidad said, highlighting the Navy’s prompt action in deploying both an aircraft and the BRP Jose Rizal to monitor the vessel.

The Russian submarine was spotted 80 nautical miles west of Cape Calavite, Occidental Mindoro.

Military response 

The Russian submarine remained surfaced and maintained communication with Philippine forces throughout its transit. 

According to the country’s Navy, the submarine’s crew informed Philippine authorities it was waiting for improved weather conditions before continuing its journey to Vladivostok, Russia.

Philippine naval forces, including the BRP Jose Rizal, closely monitored the submarine’s movement, ensuring it adhered to maritime regulations within the Philippine EEZ. Trinidad noted that the submarine displayed no aggressive behavior and complied fully with international protocols.

Under the United Nations Convention on the Law of the Sea (UNCLOS), foreign vessels are permitted to navigate through an EEZ as long as they do not extract resources, loiter, or conduct unauthorized activities such as scientific surveys. 

Malaya explained that while the EEZ grants the Philippines rights over resources, it remains part of international waters.

“EEZ rights are more about economic and natural resources. It’s still part of the high seas where any vessel can pass through, provided they respect our laws,” Malaya said in a press briefing. He emphasized that similar rights are extended to Philippine vessels navigating the EEZs of other nations.

Strategic and regional implications

The unexpected presence of the submarine has raised concerns among Philippine officials about potential risks to maritime stability. Senator Jinggoy Estrada expressed apprehension over the geopolitical implications of the incident.

“This situation is concerning, raising significant questions about the stability and security of our already volatile maritime domain, which is a flashpoint for geopolitical tensions,” Estrada said in a statement.

Estrada called on the Department of National Defense, the Armed Forces of the Philippines, and the Department of Foreign Affairs to take decisive action and clarify the submarine’s intentions.

The incident also brings renewed attention to Russia’s activities in the region. Moscow has conducted joint naval exercises with China in the South China Sea, a vital waterway where territorial disputes remain unresolved. 

China, which claims nearly the entire South China Sea, has faced pushback from its neighbors, including the Philippines, whose claims were upheld in a 2016 international tribunal ruling.

The Kilo-class submarine, which can carry Kalibr missiles widely used in Russia’s operations in Ukraine, is known for its stealth and advanced capabilities. Its operational depth of 240 meters and ability to dive up to 300 meters make it a formidable asset in contested waters.

Ensuring vigilance

Trinidad reiterated that while the submarine’s passage was consistent with international law, the incident underscores the importance of maintaining vigilance in Philippine waters. “We were surprised that something was detected, but we were able to respond, establish communication, and the conversation went well,” he said.

The Navy confirmed that the submarine was escorted out of the Philippine EEZ and was last reported heading northward toward its destination. While the incident has been resolved, officials have called for heightened monitoring and coordination to prevent potential conflicts in the future.

As regional tensions continue to simmer, the Philippines faces the challenge of balancing its sovereignty, international protocols, and evolving dynamics in a contested maritime domain.

All photos credit: Philippine Navy

Top photo: The Russian submarine UFA 490 transited through the West Philippine Sea, as photographed on November 28.