The concept of the metaverse, a virtual and interconnected world where real and digital elements coexist, is rapidly emerging as a transformative technology in various sectors. One such sector where the metaverse is making substantial inroads is in military defense applications. This book chapter provides a comprehensive exploration of the metaverse’s integration into military defense, drawing from real cases and highlighting the potential threats and challenges it presents. The metaverse continues to gain prominence in military defense, and it also brings forth a set of unique challenges and potential dangers. This chapter examines these emerging threats, including concerns related to cybersecurity, data privacy, and information warfare within the metaverse. It addresses the implications of virtual espionage, the manipulation of digital assets, and the potential for adversaries to exploit vulnerabilities within metaverse-based defense systems. By analyzing real cases and highlighting the associated risks, readers can better comprehend the transformative potential of this technology while remaining vigilant against its potential pitfalls. As military defense strategies evolve in the era of the metaverse, a thorough understanding of its applications and vulnerabilities becomes paramount for policymakers, military professionals, and technology enthusiasts alike.