Convoy OS.33 (code word "PAROLE") sailed from Liverpool at 1605 hrs. on July 1, 1942, bound for Freetown, Sierra Leone. Twenty merchant vessels sailed in line, 5 cables* apart, down the river to the end of the swept channel. There, they continued two abreast until eventually, when they were joined by vessels from Milford (8), Clyde (9) and Oban (5), they formed the full nine columns of four or five ships which was the convoy formation. In all, forty-one merchant vessels sailed around the north of Ireland bound for the South Atlantic with ten of them carrying dangerous cargoes. The Commodore (O. H. Dawson. RNR) sailed in the centre lead vessel SS Castalia (51) for Freetown while the masters of SS New Texas (71) and SS New Toronto (31) acted as Vice and Rear Commodores respectively for Takoradi, Gold Coast (now Ghana). The convoy included one Oiler, SS Laurelwood (55), to refuel the escort vessels.

In the event of any ship being damaged while in the convoy, the rear ships of the columns were designated as Rescue Ships with orders to save life and rejoin the convoy. The vessels were numbered according to the Cruising Order. Should the Commodore wish to signal any particular ship then he would hoist the appropriate ship number. Ships were instructed to maintain a distance of 3 cables* (5 cables by night) between the columns and 2 cables from the vessel in front. These distances were obtained by sextant angle from the masthead of the neighbouring vessels whose heights were noted on the Cruising Order. The normal cruising speed was 8 knots.

[* 1 cable = 100 fathoms = 600 feet]

The Liverpool contingent had only been at sea for two and a half hours when HMS Ophelia (unconnected with the convoy) was in collision with SS Ocean Honour (74) and returned to Liverpool for repairs. SS Ocean Honour, however, was only slightly damaged above the waterline and continued with the convoy.

The passage to the Azores was uneventful except that on July 10, 1942, SS Empire Attendant finally lost contact with the convoy after breaking down for the seventh time (she was later torpedoed with the loss of all hands). At 0900 hrs on July 11, 1942 the vessels bound for South America (SS Shaftesbury, SS Radcombe, SS Sithonia, SS Bruyere, SS Cortona and SS Siris) together with SS Consuelo and those bound for South Africa (SS Port Hunter, SS Glenberg, SS Dona Aurora, SS Sophocles and SS Marsdale) were detached from the convoy to proceed independently.

It was not until 1534 hrs on July 11 that the Admiralty reported to the convoy that they had picked up a radio signal from a U-boat giving a sighting report of Convoy OS.33 (at 1258 hrs). Unfortunately, the report came too late for the vessels that had been detached and nearly half of them were torpedoed and sunk.

The arrival of the convoy at Freetown was signalled at 1313Z on July 20, 1942.