High entropy alloys, as a new approach for alloy design, have attracted significant research efforts recently. One of the most promising candidates are CrMnFeCoNi and its variants. They have shown an exceptional combination of strength and ductility at cryogenic temperature. The underpinning mechanisms leading to such great properties have remained unclear. There are a few studies with EBSD/TEM at deformed states showing that twins induced by deformation may play a significant role. In situ studies are critically needed for the conformation of this mechanism. It is thus timely to use in situ neutron diffraction at EnginX combining with stress rig at reduced temperatures to determine the lattice strain evolution and twin fraction. The results will be of significance for the design of new high entropy alloys making full use of deformation induced-twin structure.