They've been dubbed China's "Little Blue Men," an allegedly Beijing-controlled maritime militia that analysts say could be hundreds of boats and thousands of crew members strong.
China doesn't acknowledge their existence and when questioned, refers to them as a "so-called maritime militia." But Western experts say the alleged militia is an integral part of Beijing's efforts to exert its territorial claims in the South China Sea and beyond.
They claim its blue-painted vessels and their crews - allegedly funded and controlled by the People's Liberation Army - can quickly bring a Chinese presence so large around disputed reefs and islands they are almost impossible to challenge without triggering a military confrontation.