The Battle of Surabaya was fought between pro-independence Indonesian soldiers and militia against British and British Indian troops as a part of the Indonesian National Revolution. The peak of the battle was in November 1945. The battle was the heaviest single battle of the revolution and became a national symbol of Indonesian resistance. Considered a heroic effort by Indonesians, the battle helped galvanise Indonesian and international support for Indonesian independence. 10 November is celebrated annually as Heroes' Day (Hari Pahlawan).