Defender Europe 21 Exercises Multinational Interoperability, Readiness, Transparency > U.S. DEPARTMENT OF DEFENSE > Defense Department News by The Editor May 4, 2021 0 Exercise Defender Europe 21 has started once again. This year's exercise involves 26 nations, including the U.S., and around 28,000 multinational forces all focused on building operational readiness and interoperability ...