'BT' (i) was the designation of Allied convoys (together with a numerical suffix) plying the route from Bahia, Brazil, to Trinidad, and as such reciprocals of the 'TB' (ii) series (January/July 1943).

The first of these 'Bahia to Trinidad' convoys was BT.1 of 18/30 January 1943 with 37 merchant vessels, and the last was BT.18 of 3/15 July 1943 with 17 merchant vessels.