The Brazilian Air Force’s KC-390 Millennium executed its first flight through the Mach Loop on 17 July 2026, marking the inaugural passage of a heavy military transport through Wales’ 13-km low-altitude training canyon [1][2]. Unlike typical Mach Loop users—fighter jets and light aircraft—the KC-390’s 26,000 kg payload capacity and Mach 0.8 cruise speed demonstrate unprecedented agility for a multi-mission airlifter [2][9]. Embraer released video footage capturing the demonstrator aircraft navigating narrow valleys at minimal altitude, underscoring tactical versatility beyond standard cargo roles [1][2]. This public demonstration, not an operational deployment, highlights the platform’s fly-by-wire digital architecture enabling precise low-level navigation previously reserved for lighter platforms [2][4]. Operators now see a medium airlifter capable of ACE-compatible maneuvers in high-risk terrain.