Operation Overlord was the codename for the Battle of Normandy, the Allied operation that launched the successful invasion of German-occupied Western Europe during World War II.
 The operation was launched on 6 June 1944 with the Normandy landings (Operation Neptune, commonly known as D-Day).
 A 1,200-plane airborne assault preceded an amphibious assault involving more than 5,000 vessels.
 Nearly 160,000 troops crossed the English Channel on 6 June, and more than two million Allied troops were in France by the end of August.
Exercise Tiger, or Operation Tiger, was the code name for one in a series of large-scale rehearsals for the D-Day invasion of Normandy, which took place in April 1944 on Slapton Sands in Devon.
 Coordination and communication problems resulted in friendly fire deaths during the exercise, and an Allied convoy positioning itself for the landing was attacked by E-boats of Nazi Germany's "Kriegsmarine", resulting in the deaths of at least 749 American servicemen.
 Because of the impending invasion of Normandy, the incident was under the strictest secrecy at the time and was only nominally reported afterwards.
The Battle of Arawe (also known as Operation "Director") was fought between Allied and Japanese forces during the New Britain Campaign of World War II.
 The battle formed part of the Allied Operation Cartwheel, and had the objective of serving as a diversion before a larger landing at Cape Gloucester in late December 1943.
 The Japanese military was expecting an Allied offensive in western New Britain, and was reinforcing the region at the time of the Allied landing in the Arawe area on 15 December 1943.
 The Allies secured Arawe after about a month of intermittent fighting with the outnumbered Japanese force.
Utah, commonly known as Utah Beach, was the code name for one of the five sectors of the Allied invasion of German-occupied France in the Normandy landings on June 6, 1944 (D-Day), during World War II.
 The westernmost of the five code-named landing beaches in Normandy, Utah is on the Cotentin Peninsula, west of the mouths of the Douve and Vire rivers.
 Amphibious landings at Utah were undertaken by United States Army troops, with sea transport, mine sweeping, and a naval bombardment force provided by the United States Navy and Coast Guard as well as elements from the British, Canadian, Dutch and other Allied navies.
Operation "Bodyguard" was the code name for a World War II deception plan employed by the Allied states before the 1944 invasion of north-west Europe.
 The plan was intended to mislead the German high command as to the time and place of the invasion.
 The plan contained several operations, which culminated in the tactical surprise of the Germans during the Normandy landings on June 6, 1944 (also known as D-Day) and delayed German reinforcements to the region for some time afterwards.
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.
Johann-Nielsen Jebsen, Nickname "Johnny", was an anti-Nazi German intelligence officer and British double agent (code name Artist) during the Second World War.
 Jebsen recruited Dušan Popov (who became the British agent Tricycle) to the Abwehr and through him later joined the Allied cause.
 Kidnapped from Lisbon by the Germans shortly before D-Day, Jebsen was tortured in prison and spent time in a concentration camp before disappearing, presumed killed, at the end of the war.
José M. Cabanillas (September 23, 1901 – September 15, 1979), was a rear admiral in the United States Navy who as an executive officer of the USS "Texas" participated in the invasions of North Africa and the Battle of Normandy (also known as D-Day) during World War II.
Operation Bolero was the commonly used reference for the code name of the United States military troop buildup in the United Kingdom during World War II in preparation for the initial cross-channel invasion plan known as Operation Roundup, to be implemented in mid-1943, or for its lesser contingency alternative, Operation Sledgehammer, to be executed in the fall of 1942 in the event of German setbacks or to ease Axis pressure on the Eastern Front.
 ("Bolero" was the code name used in official communications to stand in for "United Kingdom" when describing the theater or movements.)
 What later became the Bolero plan – the buildup of a strategic air force in Great Britain in preparation for Roundup – was first submitted by Commanding General of the U.S. Army Air Forces, Henry H. Arnold, to General George Marshall, the U.S. Army Chief of Staff, on April 12, 1942, and set in motion a huge movement of men and material that laid the groundwork for Operation Overlord.
Operation Jupiter was the code name for a plan originating in 1941 for an invasion of northern Norway and Finland by Allied forces during the Second World War.
 The first versions of the plan were code named Operation Dynamite, Operation Ajax and Operation Marrow.
 Devised and vigorously promoted by Sir Winston Churchill, the Prime Minister of the United Kingdom, the plan was opposed by all the senior British and Allied commanders, who considered it impractical because of insufficient air support and of limited value.
 The scheme was eventually abandoned in favour of the Normandy landings.

Question: What was the code name for this Allied operation in WWII, also known as D-Day?
Answer: Operation Overlord