This was the designation of Allied fast convoys (together with a numerical suffix) plying the route from Halifax, Nova Scotia, to Liverpool or Dover in the UK (September 1939/February 1940).
The series catered for vessels returning from the Panama Canal or the Caribbean whose speed was greater than the 9 kt of the 'HX' series but less than the 13 kt required to sail independently. There were 17 such convoys, which were fast sections of 'HX' convoys.
The first of them was HXF.1 of 19/29 September 1939 with the 13,867-ton British Antonia, 15,501-ton British Arandora Star, 16,297-ton British Cameronia, 28,124-ton French Champlain, 13,391-ton French Colombie, 18,435-ton French De Grasse, 20,022-ton British Duchess of Richmond and 15,495-ton British Orbita, escorted by the heavy cruisers Berwick and York, and destroyers Amazon, Fraser and Canadian Saguenay. The three French ships proceed to Le Havre rather than Liverpool.
The last of the series was HFX.20 of of 12/25 February 1940 with the 5,218-ton British Beignon, 4,721-ton Norwegian Emma Bakke, 2,749-ton Swedish Hallaren, 9,973-ton Norwegian Italia, 5,343-ton British Manchester Commerce, 5,277-ton British Manchester Exporter, 5,495-ton British Salacia, 7,365-ton British San Adolfo detached to Devonport and 7,199-ton British Tudor Star, escorted by the armed merchant cruiser Laconia and destroyers Acasta, Fraser, Venetia and Canadian St Laurent.