The Future Railway Mobile Communication System (FRMCS) will be the 5G worldwide standard for railway operational communications, conforming to European regulation as well as responding to the needs and obligations of rail organisations outside of Europe. The work on functional & technical requirements, specification & standardisation in 3GPP as well as regarding harmonised spectrum solutions is currently led by UIC, in cooperation with the whole railway sector. A major challenge is the update by European Railway Agency of the Technical Specifications for Interoperability of Control Command and Signalling (CCS TSI) by the end of 2022 with a full description of FRMCS with respect to interoperability functions. Therefore, the 5GRAIL project aims to verify the first set of FRMCS specifications and standards (FRMCS V1) by developing and testing prototypes of the FRMCS ecosystem. The validation of the latest available railway-relevant 5G specifications will be achieved through cross-border emulation trials covering significant portions of railway operational communication requirements and including the core technological innovations for rail expected from 5G release 16 and pre-release 17. The project will first define functional tests and then work towards the development and evaluation of prototypes, for both on-board and infrastructure, including vital (ETCS, ATO) and essential (voice specific services, TCMS and video) applications. Prototypes will be then tested in simulated and real environments, with pilots in labs and in the field rolled out in various European sites (France, Hungary and Germany), to ensure compliancy and validation for FRMCS specifications, standards and performance, and consequently guarantee the time to market for FRMCS deployments, planned for 2025 as per European timeline. 5GRAIL will finally deliver test report conclusions to potentially update FRMCS V1 specifications and to identify technical constraints related to implementation issues.