Chilly Harbor The guided missile destroyer USS Oscar Austin transits the harbor in Tromsø, Norway, prior to the start of Exercise Formidable Shield 2023, May 4, 2023. Formidable Shield is a biennial integrated air and missile defense exercise involving a series of live-fire events against subsonic, supersonic, and ballistic targets. SHARE: Download: Full Size (1.55 MB) Tags: navy, missile defense, Formidable Shield Credit: Navy photo VIRIN: 230504-N-NO901-2001A.JPG Photo Gallery