The 1st Hazardous Environment Combat Unit, often abbreviated as "1-HECU" or "1st HECU", is a United States Marine Corps special operations unit specially trained to deal with a variety of indoor combat situations, particularly involving a dangerous environment and unconventional enemies.

Active: 2011–

Country: United States.

Branch: United States Marine Corps.

Type: Special operations force.

Roles:
Foreign internal defense.
Special reconnaissance.
Direct action.
Counter-terrorism.
Unconventional warfare.

Size: Classified.

Part of: Marine Corps Special Operations Command and United States Special Operations Command

HQ: Santego Military Base, Arizona.