On 2 December 1941 — as Japanese aggression was expected shortly and the small, lightly armed ship could not hope to combat the overwhelming odds facing her in China — the gunboat received orders to sail to the Philippines with Luzon Stevedoring tugboat Ranger to catch up with her later.

Immediately going to general quarters, the crew remained near their guns throughout the passage, and on 9 December intercepted and sank a small Japanese trawler (South Advance Maru No.

3), 50 miles northwest of Bolinao, Pangasinan at 16°42′N 118°53′E / 16.700°N 118.883°E / 16.700; 118.883,[2] taking 10 prisoners-of-war, among the first taken by Americans in World War II (the first POW was Kazuo Sakamaki, sole survivor of the midget submarine attack on Pearl Harbor).

The shortage of fuel in the Philippines ended these patrols in early March, and the ships instead took turns watching for Japanese small craft at a position 3 miles east of Corregidor.

When the naval situation in Manila Bay appeared hopeless, Mindanao’s crew was ordered ashore on 10 April to help defend Fort Hughes.