SD-4's location in Paris on a CIA briefing map
SD-4 was a branch of the Alliance of Twelve based out of Paris, France.
SD-4 operated a surveillance camera monitoring financial offices in Cape Town, South Africa. A man presumed to be Igor Valenko/Calder was captured on surveillance footage, corroborating Sydney Bristow's theory about him. (Snowman)
When Marshall Flinkman was abducted by Cuvee's operatives, Arvin Sloane had his access codes changed and contacted SD-4 to have a new Operations Technician transferred to SD-6 to replace Marshall. (A Higher Echelon)
Just prior to gaining access to server 47, Assistant Director Kendell noted in a briefing that the CIA was aware of the location 7 of the 12 SD cells, including SD-4 in Paris. During the CIA operation to bring down all Alliance SD cells, a female agent noted that the SD-4 team was standing by; and later noted at least 2 agents were down during the siege on SD-4, but like all SD cells, SD-4 was in safely in control of the authorities after the operation. (Phase One)