This was the designation of Allied troopship and fast transport convoys (together with a numerical suffix) plying the route from New York to the Netherlands West Indies, except CU.1 to CU.8, which were eastbound convoys of 14-kt tankers, and fast merchant ships plying from Curaçao to the UK, and as such reciprocals of the 'UC' series (March 1943/June 1945).
There were 74 of these 'Curaçao to the UK' convoys, of which the earliest comprised tankers sailing directly from petroleum refineries at Curaçao to the UK. Most convoys of the series assembled in New York City and included fast freighters and troopships with tankers arriving from Aruba via TAG convoys to Guantánamo Bay and GN convoys from Guantánamo to New York.
Allied matériel had been transported from North America to the UK in HX convoys since 1939 and in slower SC convoys since 1940 under escort of British and Canadian warships. The US Navy provided a few escorts to HX and SC convoys from September 1941 to April 1943. The rationale for the CU convoys, which were schemed as an emergency measure, was the maintenance of adequate petroleum fuel reserves in the UK for the continued strategic bombing of Europe following the heavy losses of tankers along the east coast of North America during ‘Paukenschlag’. Modern tankers could travel faster than the 9-kt HX convoys, and the CU convoys were continued as fast (14-kt) convoy series along the HX convoy route. US destroyer escorts provided anti-submarine screens for CU convoys because the ‘Flower’ class corvettes of the Mid-Ocean Escort Force were not fast enough to escort these convoys, undertake anti-submarine operations when the convoys were attacked, and then resume their positions as escorts once again.
Most of the CU and reciprocal UC convoys were screened by four to six destroyer escorts.
Nine US tankers (10,169-ton Caribbean, 10,198-ton Colina, 10,907-ton E. W. Sinclair, 10,169-ton Esso Paterson, 11,236-ton US Esso Philadelphia as the escort oiler, 10,169-ton Esso Wilmington, 9,298-ton Oklahoma, 10,180-ton Sparrows Point and 10,944-ton Virginia) departed Curaçao as the CU.1 convoy on 20 March 1943 with an escort that included at various times 10 escorts, and reached Liverpool on 1 April.
Additional sailings from Curaçao were CU.2 in June, CU.3 in July, CU.4 in September, and CU.6 in November. CU.5 was the first to originate in New York on 13 October 1943. Approximately three or four CU convoys sailed from New York each month between December 1943 and May 1945, and the CU.23, CU.24, CU.28, CU.30, CU.33, and CU.35 convoys included troopships and were sometimes identified a TCU convoys. The CU.24 convoy, for example, sailed in two sections with troopships in the TCU.24A element and ammunition ships in the TCU.24B element. A total of 2,255 ships crossed the Atlantic in CU convoys, and the CU.73 convoy was the last to depart New York on 30 May 1945 with the 26,9453-ton British Britannic and 20,175-ton British Franconia, escorted by the US destroyer Davis and the destroyer escorts Menges and Pride, and reached Liverpool on 8 June.