When World War I began, Armstrong-Whitworth were completing the battleship Sultan Osman I for the Ottoman Empire; it had originally begun as Rio de Janeiro for Brazil.

To avoid the ship being used by Britain's enemies the battleship was seized and subsequently completed for the RN as HMS Agincourt and served in the Royal Navy in World War I.

The secondary armament for each supplied by Armstrongs were 12 6-inch 50-calibre guns, which were designated 6-inch BL Mk XVII in British service.

When World War I began, Armstrong-Whitworth were building the coast defence ships Nidaros and Bjørgvin for Norway.

Aft 6-inch gun displayed on HMS M.33 (at Portsmouth Historic Dockyard, UK) is from Almirante Latorre (ex-Canada) donated to the ship from Chile in 2000.

Two pieces of 6-inch mark XVII coastal defense guns are to be seen at the "Mirador Punta Angamos", close to Mejillones, Chile.