When the Second World War erupted, Gumbay Piang, along with fellow Moro leaders such as Salipada Pendatun, organized the famed resistance group named the Moro-Bolo Battalion during the Japanese occupation of the Philippines to fight the Japanese. The insignia of the group was the bolo and the kris, the respective weapons of Christian and Muslim populations, respectively, symbolizing a united front against the Japanese aggressors. The Moro-Bolo Battalion consisted of about 20,000 men. Gumbay Piang's Cotabato Moros used Bolo knives to fight the Japanese, and swore that they would "fight to the last".