Red Ensign
After the Anglo-Boer War from 1899 to 1902 until the formation of the Union of South Africa in 1910, the British Union Flag was the national flag in the four British colonies that became South Africa.
As was the case throughout the British Empire, the Red and Blue Ensigns were the official flags for merchant and government vessels at sea, and the British Admiralty authorised them to be defaced with the shield of the South African coat of arms.[2][3] These ensigns were not intended to be used as the Union's national flag, although they were used by some people as such.