The main port , Walvis Bay , and the Penguin islands were annexed by Britain as part of the Cape Colony in 1878 , and became part of the Union of South Africa in 1910 .
The main port city , Walvis Bay , and the Penguin Islands were annexed by Great Britain in 1878 as a part of the Cape Colony , which became a part of the Union of South Africa on 31 May 1910 .