'CO' was the designation of Allied convoys (together with a numerical suffix) plying the route from Newcastle to Melbourne and Adelaide, Australia, and as such reciprocals of the 'OC' series (June 1942/December 1943).

The first of these 150 convoys was CO.1 of 8/14 June 1942 with the 4,734-ton British Age, 3,279-ton British Allara, 5,482-ton Greek George M. Livanos, 7,113-ton British Hauraki, 4,584-ton British Iron Baron, 4,368-ton British Macedon, 2,417-ton British Meroo, 7,006-ton British Scottish Chief, 4,815-ton Greek Theofano Livanos and 5,181-ton Norwegian Vito escorted by the Australian destroyer Arunta and minesweeper Kalgoorlie.

The last was CO.149 of 4/7 December 1943 with the 4,239-ton British Barrosa, 5,259-ton British Helen Moller, 4,375-ton Yugoslav Olga Topic, 1,892-ton British Wear, and 7,176-ton US Wilbur Wright escorted by the Australian minesweeper Ballarat and auxiliary patrol vessel Wilcania.