JOINT BASE PEARL HARBOR-HICKAM (June 4, 2021) The Los Angeles-class fast-attack submarine USS Chicago (SSN 721) departs Joint Base Pearl Harbor-Hickam for Exercise Agile Dagger 2021 (AD21). AD21 is a training exercise, with one-third of the Pacific Submarine Force getting underway, to assess warfighting readiness and build capacity for the joint force. (U.S. Navy photo by Mass Communication Specialist 1st Class Michael B. Zingaro)