High-Priority Mission

A High-Priority Mission is an operation dubbed by XCOM's top soldiers to be a massively important task for one reason or another.

The first High-Priority Mission during the Enemy Unknown campaign was Operation: Bloodied Gauntlet, which saw the aliens perform a Terror Attack against Manehattan resulting in the deaths of hundreds of innocents, including Winter Glow (Bradford's mother). XCOM responded, losing two of their own, but received help from a new elite Midnight Paladin team known as DEMISE.

The first High-Priority Mission during the Enemy Reborn campaign was Operation: Gatecrasher, where in XCOM took it's only chance to perform against ADVENT for the first time, resulting in all four operatives becoming wounded (though thankfully, not fatally).

The units who can dub a mission "High-Priority" are Commander Fielde Locke, Central Officer John Bradford, and the Councilman. Other units may suggest a mission should be High-Priority, but it's ultimately up to one of the three to decide.

When a High-Priority Mission is underway, XCOM usually deploys it's best team combination with no regard for training new blood. Due to the importance of these missions, XCOM also allows for full deployment of all forces whether they are wounded or not, though forces will not be deployed if they are Critically Wounded or Gravely Wounded, or otherwise not available (Infiltrating, Captured).

Enemy Unknown Missions
All Terror Attacks

Operation: Home Plate - The assault on the Alien Base founded in the Frozen North

Operation: Ashes and Temples - The defence of XCOM HQ in the Badlands from alien forces

Operation: Avenger - The assault on the Alien Temple Ship

Enemy Reborn Missions
All Haven Strikes

Operation: Gatecrasher - The first XCOM assault against ADVENT

Operation: Prodigy - The investigation of an ADVENT facility and rescue of Union Strike

Operation: Hierarchy - The investigation of a possible signal from Sunset Shimmer's counterpart

Operation: Last Gift - The investigation of a possible signal from Sunset Shimmer's counterpart

Operation: Dogfight - The assault on a still-airborne ADVENT Supply Barge

Operation: Der Reise - Investigation of Monument development facility

Operation: Zetsubou No Shima - Investigation of abandoned Haven infested by Chryssalids

Operation: Gorod Krovi - Assault on ECOM HQ in the ruins of Stalliongrad

Operation: Cryptic Vanguard - Assault on Cypher Development Facility

Operation: Burning Wishes - Failed defence of the Avenger from ADVENT forces

Operation: Phoenix - XCOM's final chance against ADVENT with all assets in play