Under the Navy's Flexible Cyber-Secure Radio (FlexCSR) program, the Naval Information Warfare Center Pacific and the Massachusetts Institute of Technology's Lincoln Laboratory are jointly developing a unique cybersecurity solution for tactical unmanned systems (UxS): the FlexCSR Security/Cyber Module (SCM) End Cryptographic Unit (ECU). To deal with possible loss of unmanned systems that contain the device, the SCM ECU uses only publicly available Commercial National Security Algorithms and a Tactical Key Management system to generate and distribute onboard mission keys that are destroyed at mission completion or upon compromise. This also significantly reduces the logistic complexity traditionally involved with protection and loading of classified cryptographic keys. The SCM ECU is on track to be certified by the National Security Agency for protecting tactical data-in-transit up to Secret level. The FlexCSR SCM ECU is the first stand-alone cryptographic module that conforms to the United States Department of Defense (DoD) Joint Communications Architecture for Unmanned Systems, an initiative by the Office of the Secretary of Defense supporting the interoperability pillar of the DoD Unmanned Systems Integrated Roadmap. It is a credit card-sized enclosed unit that provides USB interfaces for plaintext and ciphertext, support for radio controls and management, and a software Application Programming Interface that together allow easy integration into tactical UxS communication systems. This paper gives an overview of the architecture, interfaces, usage, and development and approval schedule of the device.