Marine Fighter Attack Squadron 121 (VMFA-121), also known as the "Green Knights", is a United States Marine Corps aircraft squadron operating the F-35B Lightning II. The squadron is based at Marine Corps Air Station Yuma, Arizona and falls under the command of Marine Aircraft Group 13 (MAG-13) and the 3rd Marine Aircraft Wing (3rd MAW). Their tail code is VK and their radio call sign is "Combat".