Coombe defended residents of the Barossa Valley during World War I who were suspected of disloyalty and were persecuted because of their German heritage. He opposed anti-German measures such as the closure of Lutheran schools. He opposed conscription and the "intimidation of male voters in the referendum of 1917" He collapsed during a public meeting at Port Adelaide in support of this campaign at the Semaphore and died of a cerebral haemorrhage a week later without recovering consciousness. He was buried at Willaston.