The project aims at strengthening Copernicus Marine Service in the areas of regional ocean uncertainty modelling, Ensemble-based multiresolution forecasting, and Ensemble-based multigrid data assimilation. The work is based on stochastic modelling of ocean physics and includes methods suitable to assess the forecasting skill for high-resolution dynamics of the Blue Ocean. The work builds upon, and expands, the previous Service Evolution projects SCRUM and SCRUM2. In a first step, we will set up a multigrid configuration derived from the IBI36 MFC to generate Ensembles using appropriate hypotheses for sources of error, will define Ensemble forecasting metrics, and will assess the added value of downscaling and local grid refinement. In a second step, we will focus on data assimilation, performing incremental analysis to assess the added value of multigrid Ensemble covariances for analysis and forecasting. Overall, we wish to contribute to the Copernicus Marine Service Data Assimilation team guidance in support of upcoming decisions regarding the evolution of high-resolution, multigrid forecasting performance as well as regional data assimilation schemes in Copernicus Marine.