LISBON, Portugal (May 19, 2021) The Portuguese navy submarine NRP Tridente (S160) departs Lisbon, Portugal to participate in NATO Exercise Steadfast Defender 2021, May 19, 2021.Steadfast Defender is a defensive exercise based on an Article 5 scenario which is designed to deter aggression and respond to crisis if necessary. (Photo courtesy of the Spanish navy by Petty Officer Laura Pons Miles)