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 original plan was for the SAS team to march to the Rio Grande air base and set up an observation post to collect intelligence on the base's defences.

The mission required that the Sea King helicopter travel a distance close to its operation range, so this would be a one-way mission.
Therefore, the aircrew mission consisted of dropping the SAS team in Argentina, heading to Chile and disposing of the aircraft by sinking it in deep water.

The aircraft, with a three-man crew and eight-man SAS team, took off from Invincible at 0015 hrs on 18 May. Due to an unexpected encounter with a drilling rig in an offshore gas field it was forced to detour, adding twenty minutes to the transit.
As it approached the Argentinian coast after four hours, fog reduced flying visibility to less than a mile.
As they approached twelve miles from the planned SAS drop-off point, visibility was reduced to such an extent that the pilot was forced to land.
The pilot and the commander of the SAS patrol disagreed on their exact position while the SAS commander was also certain that they had been spotted by an Argentine patrol: he asked to be dropped on the Chile/Argentine border.
The pilots were forced to fly on instruments through Instrument Meteorological Conditions into neutral Chile.
The SAS team was dropped off on the south coast of Bahia Inútil where they were to attempt to move to their observation post on foot.
The helicopter crew flew to a beach closer to Punta Arenas where they landed.
One of the two pilots and the aircrewman disembarked on the beach.
They cut holes in the helicopter to allow it to sink once it was ditched.
The other pilot then flew it out over the water but was unable to sink it.
He flew back to the beach in order to cut more holes, but was blinded in his night vision goggles by a blinking "Low Fuel" light and crashed on the beach.
The crew set fire to the helicopter and detonated explosive charges before leaving the scene.
They moved over the course of several nights to a point of observation near Punta Arenas, where they attempted to make contact with the British Embassy.
They were discovered and picked up by the Chilean military while moving through town, and were turned over to British officials.

According to Argentine reports, on the night of 17/18 May, the helicopter was tracked by the radar of the destroyer ARA Bouchard, which sent a message to her sister ship ARA Piedrabuena patrolling on the north, and then to the air base of Río Grande.
Members of the Argentine 24th Regiment of Infantry claimed in 2007 that they hit the helicopter with small arms fire amid thick fog south of Rio Gallegos.
The SAS reconnaissance mission was eventually aborted.
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 original plan was for the SAS team to march to the Rio Grande air base and set up an observation post to collect intelligence on the base's defences.
The mission required that the Sea King helicopter travel a distance close to its operation range, so this would be a one-way mission. Therefore, the aircrew mission consisted of dropping the SAS team in Argentina, heading to Chile and disposing of the aircraft by sinking it in deep water. 
The aircraft, with a three-man crew and eight-man SAS team, took off from Invincible at 0015 hrs on 18 May. Due to an unexpected encounter with a drilling rig in an offshore gas field it was forced to detour, adding twenty minutes to the transit. As it approached the Argentinian coast after four hours, fog reduced flying visibility to less than a mile. As they approached twelve miles from the planned SAS drop-off point, visibility was reduced to such an extent that the pilot was forced to land. The pilot and the commander of the SAS patrol disagreed on their exact position while the SAS commander was also certain that they had been spotted by an Argentine patrol: he asked to be dropped on the Chile/Argentine border. The pilots were forced to fly on instruments through Instrument Meteorological Conditions into neutral Chile. The SAS team was dropped off on the south coast of Bahia Inútil where they were to attempt to move to their observation post on foot. The helicopter crew flew to a beach closer to Punta Arenas where they landed. One of the two pilots and the aircrewman disembarked on the beach. They cut holes in the helicopter to allow it to sink once it was ditched. The other pilot then flew it out over the water but was unable to sink it. He flew back to the beach in order to cut more holes, but was blinded in his night vision goggles by a blinking "Low Fuel" light and crashed on the beach. The crew set fire to the helicopter and detonated explosive charges before leaving the scene. They moved over the course of several nights to a point of observation near Punta Arenas, where they attempted to make contact with the British Embassy. They were discovered and picked up by the Chilean military while moving through town, and were turned over to British officials.
According to Argentine reports, on the night of 17/18 May, the helicopter was tracked by the radar of the destroyer ARA Bouchard, which sent a message to her sister ship ARA Piedrabuena patrolling on the north, and then to the air base of Río Grande. Members of the Argentine 24th Regiment of Infantry claimed in 2007 that they hit the helicopter with small arms fire amid thick fog south of Rio Gallegos. The SAS reconnaissance mission was eventually aborted.
Operation Mikado