Question: Which operation, part of the Invasion of Normandy, was conducted by the fictitious allied army group to deceive the Germans about where the Allies would land in preparation for Operation Overlord?

Context paragraphs:
Operation Quicksilver (deception plan): Operation Quicksilver was a Second World War military deception.  Undertaken by the Allies in 1944, the operation threatened an invasion of France in the Pas de Calais region through the simulation of a large Field Army in South East England.  Quicksilver formed part of the Operation Fortitude deception, itself part of the strategic Operation Bodyguard plan.  The key element of Quicksilver was the creation in German minds that "First United States Army Group" (FUSAG) commanded by General George Patton supposedly would land in the Pas-de-Calais for the major invasion of Europe, after the landings in Normandy had lured the German defenders to that front.  (FUSAG was a genuine army group headquarters which later became Omar Bradley's 12th Army Group, but was given a fictitious role and many non-existent divisions for purposes of deception.)

Normandy landings: The Normandy landings (codenamed Operation Neptune) were the landing operations on Tuesday, 6 June 1944 (termed D-Day) of the Allied invasion of Normandy in Operation Overlord during World War II.  The largest seaborne invasion in history, the operation began the liberation of German-occupied northwestern Europe from Nazi control, and contributed to the Allied victory on the Western Front.

D-Day naval deceptions: Operations Taxable, Glimmer and Big Drum were tactical military deceptions conducted on 6 June 1944 in support of the Allied landings in Normandy.  The operations formed the naval component of Operation Bodyguard, a wider series of tactical and strategic deceptions surrounding the invasion.  Small boats, along with aircraft from RAF Bomber Command, simulated invasion fleets approaching Cap d'Antifer, Pas-de-Calais and Normandy.  Glimmer and Taxable played on the German belief, amplified by Allied deception efforts over the preceding months, that the main invasion force would land in the Calais region.  Big Drum was positioned on the western flank of the real invasion force to try to confuse German forces about the scale of the landings.  These operations complemented Operation Titanic, which was intended to confuse the Germans about the D-Day airborne forces.

Operation Waterfall: Operation Waterfall was part of Operation Mincemeat, which was a deception to try to trick the Germans into thinking the Allies would land somewhere else in the Mediterranean other than Sicily, where they were going to land.  It involved creating a decoy army in the eastern Mediterranean to make it look like they were targeting the Balkans.  The Anglo-American force also created some dummy inflatable tanks and vehicles.

Operation Dragoon: Operation Dragoon (initially Operation Anvil) was the code name for the Allied invasion of Southern France on 15August 1944.  The operation was initially planned to be executed in conjunction with Operation Overlord, the Allied landing in the Normandy, but the lack of available resources led to a cancellation of the second landing.  By July 1944 the landing was reconsidered, as the clogged-up ports in Normandy did not have the capacity to adequately supply the Allied forces.  Concurrently, the French High Command pushed for a revival of the operation that would include large numbers of French troops.  As a result, the operation was finally approved in July to be executed in August.

Invasion of Normandy: The Western Allies of World War II launched the largest amphibious invasion in history when they assaulted Normandy, located on the northern coast of France, on 6 June 1944.  The invaders were able to establish a beachhead as part of Operation Overlord after a successful "D-Day," the first day of the invasion.

First United States Army Group: First United States Army Group (often abbreviated FUSAG) was a fictitious (paper command) Allied Army Group in World War II prior to D-Day, part of Operation Quicksilver, created to deceive the Germans about where the Allies would land in France.  To attract Axis attention, prominent US general George S. Patton was placed in command of the fabricated formation.

Operation Ironside: Operation Ironside was a Second World War military deception undertaken by the Allies in 1944.  It formed part of Operation Bodyguard, a broad strategic deception plan instigated by the Allies throughout the year to help cover the June 1944 invasion of Normandy.  Ironside supported the overall deception by suggesting to the Germans that the Allies would subsequently land along the Bay of Biscay.  It complemented efforts to deceive the Germans into believing that the Allies would also land in southern France at this time (Operation Vendetta).  Bordeaux was an important port for the German war effort and had already been a target of commando raids two years earlier.  Ironside intended to play on German fears of an invasion in the region, with the aim of tying down defensive forces following Operation Overlord in June 1944.

American airborne landings in Normandy: The American airborne landings in Normandy were the first American combat operations during Operation Overlord, the invasion of Normandy by the Western Allies on June 6, 1944, during World War II.  Around 13,100 American paratroopers of the 82nd and 101st Airborne Divisions made night parachute drops early on D-Day, June 6, followed by 3,937 glider troops flown in by day.  As the opening maneuver of Operation Neptune (the assault operation for Overlord) the two American airborne divisions were delivered to the continent in two parachute and six glider missions.

21st Army Group: The 21st Army Group was a World War II British headquarters formation, in command of two field armies and other supporting units, consisting primarily of the British Second Army and the First Canadian Army.  Established in London during July 1943, under the command of Supreme Headquarters Allied Expeditionary Force (SHAEF), it was assigned to Operation Overlord, the Western Allied invasion of Europe, and was an important Allied force in the European Theatre.  The 21st Army Group operated in Northern France, Luxembourg, Belgium, the Netherlands and Germany from June 1944 until the end of the war in Europe in May 1945, after which it was redesignated the British Army of the Rhine (BAOR).

Supporting paragraphs: First United States Army Group Invasion of Normandy
Answer: Operation Quicksilver