On 23 April, the British learned through radio intercepts that an Argentinian submarine was approaching South Georgia. This was the GUPPY II–converted Balao class , the former USS "Catfish", part of Argentina's submarine fleet of four boats. On 9 April "Santa Fe", commanded by Corvette Captain Horacio Bicain, left Mar del Plata with eleven technicians to restore utility services on New Georgia and nine marines with Bantam anti-tank missiles to reinforce the original invading force, which was armed only with rifles and machine guns. The mission was launched by Vice-Admiral Juan Lombardo, following a request for reinforcements by Captain Trombetta shortly after the Argentine invasion of South Georgia. This contradicted the military junta's orders to not reinforce South Georgia, but when Admiral Jorge Anaya, Commander-in-Chief of the Argentine Navy, learned of the mission, he refused to disavow his subordinates and authorised it. Storm conditions prevented use of the snorkel, which placed unexpected demands on the batteries and required remaining surfaced during part of the approach. Her sensors were unreliable, and the charge capacity of her aged batteries was much reduced from their original design. While undertaking her transport mission, "Santa Fe"'s orders were to remain undetected, not to attack any ships and to break contact with any ship which might detect her.