Complex sentence: The arms were then used to create the South Africa Red Ensign used unofficially as the national flag of South Africa until 1928 when the Oranje, Blanje, Blou was adopted though the South Africa Red Ensign continued to be used as the merchant ensign until 1951.
Split into simpler sentences: The arms were then used to create the South Africa Red Ensign used unofficially as the national flag of South Africa until 1928 when the Oranje, Blanje, Blou was adopted. Though the South Africa Red Ensign continued to be used at sea as the merchant ensign until 1951.