'XB' was the designation of Allied convoys (together with a numerical suffix) plying the route from Halifax, Nova Scotia, to Boston or the Cape Cod Canal, Massachusetts, and as such reciprocals of the 'BX' series (March 1942/May 1945).

The first of 196 such convoys was XB.1 of 18/20 March 1942 with the 1,908-ton Norwegian Aun, 4,883-ton Norwegian Brimanger, 8,453-ton British British Harmony, 2,833-ton British Empire Carey, 5,507-ton British Empire Cheetah, 3,849-ton British Fort Amherst, 2,642-ton Norwegian Ingertre, 8,194-ton British Lady Rodney, 1,383-ton Norwegian Magnhild, 2,637-ton US Norluna, 1,909-ton British Sonja Maersk, 2,708-ton British Uskside, 2,864-ton Polish Zagloba, and 5,790-ton US commissioned store ship Yukon.

The last convoy was XB.165 of 23/25 May 1945 with the 6,136-ton Polish Chomedy, 2,874-ton British Dufferin Park, 3,489-ton British Fort Townshend, 1,243-ton Norwegian Gulhaug and 2,875-ton British Mayfair Park, escorted by the Canadian corvette Frontenac and minesweeper Port Hope.