The Philippine Inquirer reported on Friday that a Philippine Coast Guard patrol boat, the BRP Sindangan, encountered some form of signal jamming last week while patrolling in the South China Sea.
Given the location, suspicions immediately turned to the Chinese military as the source of the jamming signal.
“We could not communicate with our vessel by satellite phone at some point during their patrol in the Spratly Islands. The signal was jammed,” an anonymous coast guard official told the Inquirer. The official explained Philippine ships often use satellite phones to communicate because their radios have limited range.
The Spratly Islands are a disputed chain that falls partially inside the Philippines’ exclusive economic zone, but China claims the entire region and has effectively occupied and militarized some of the islands. Filipino fishermen have lately complained about a Chinese tactic known as the “cabbage strategy,” in which a huge swarm of nominally civilian Chinese trawlers with paramilitary crews surround disputed islands and prevent the Filipinos from fishing there.
According to the Inquirer’s source, the Sindangan was sailing near Panganiban Reef, known to American sailors as Mischief Reef, and the Ayungin Shoal (Second Thomas Shoal) when its signal was jammed.
Panganiban Reef is one of the islets China has occupied and artificially enhanced into a fortress, while the Filipinos are hanging on to Ayungin Shoal through the unusual tactic of keeping a small crew permanently stationed on a wrecked ship called the BRP Sierra Madre that ran aground 20 years ago.
The Philippine Coast Guard official who spoke to the Inquirer said the Sindangan incident was only the latest example of Philippine ships encountering signal jamming as they sail through the Spratlys. Other Coast Guard vessels have reported satellite phone jamming near Panatag Shoal, also known as Scarborough Shoal, the scene of a major territorial dispute between China and the Philippines that escalated into a lawsuit in April.
The U.S. military has been aware for some time that China installed powerful signal jamming equipment on its militarized islands in the South China Sea. The U.S. Navy warned that China’s equipment could present a considerable safety risk to ships in the area, although the Navy indicated its top-of-the-line vessels and manned aircraft can defeat the jammers if necessary. Concerns were raised that drone aircraft could be more vulnerable.