On March 8, 1900, the shipping companies Union Steamship Company Ltd. joined forces. ( Union Line , founded 1857) and Castle Mail Packet Company Ltd. ( Castle Line , founded 1862) to create the new Union-Castle Line. The ships of both companies became the property of Union-Castle Line.
The 12,546 GRT steamship was still built under the name Celt by Harland & Wolff in Belfast , Northern Ireland , but was launched as Walmer Castle on July 6, 1901 for the new shipping company. The 173.9 meter long and 19.6 meter wide ship had two chimneys, two masts and two propellers . Until then, she was the largest ship on the Union-Castle Line. It was completed on February 20, 1902 and shortly thereafter left for its maiden voyage. Two sister ships were added later, the Armadale Castle (12,973 GRT) in 1903 and the Kenilworth Castle (12,974 GRT) in 1904 .
Like her two sister ships, the Walmer Castle was propelled by two quadruple expansion steam engines producing 12,000 PSi and a top speed of 16.5 knots. 336 passengers of the first, 174 of the second and 244 of the third class could be accommodated. After the end of the Second Boer War , the Walmer Castle was one of nine ships on the Union-Castle Line that maintained a weekly mail service to South Africa. In 1910 Herbert Gladstone, 1st Viscount Gladstone, Governor General of the Union of South Africa from 1910 to 1914, traveled aboard the ship. The ship remained in service for years until it arrived in Blyth on February 8, 1932 and was scrapped at the Hughes Bolckow Shipbreaking Company.