[7] A preliminary reconnaissance mission on Río Grande, code-named Operation Plum Duff, was launched from HMS Invincible on the night of 17/18 May, as a prelude to the attack.

The operation consisted of transporting a small SAS team to the Argentine side of Tierra del Fuego on a stripped down Royal Navy Westland Sea King HC.4.

The aircraft inadvertently passed close to an Argentinian drilling rig in an offshore gas field forcing it to detour, adding twenty minutes to the transit.

[4][11] In 2007 members of the Argentine 24th Infantry Regiment claimed that they had hit the helicopter with small arms fire amid thick fog south of Rio Gallegos.

[2] As a consequence, the airborne assault plan attracted considerable hostility from some members of the SAS, which ultimately led to one sergeant submitting his resignation shortly before the team was due to fly out to Ascension and to the squadron's commander being relieved and replaced by the regiment's second-in-command.

[2][4] The lack of on-site intelligence meant that the British forces did not have a clear idea of how Rio Grande was defended, nor any guarantees that the Super Etendards or the Exocets would even be there if an operation took place.

[2][4] The Argentine Navy claims that the Bouchard had shelled a submarine and a number of inflatable boats while on patrol two miles off Rio Grande, at the position 53°43′38.04″S 67°42′0″W / 53.7272333°S 67.70000°W / -53.7272333; -67.70000 on the evening of 16 May 1982.

[3] After the war, it was revealed that the Rio Grande area was defended by four Argentine Navy Marine Corps battalions, some of whose officers had been trained in the UK by the SBS years earlier.