Operation: TENDRIL was a UNSC operation. Not much is known about this operation, other than that Dr. Catherine Halsey knew something about it due to the fact that it is mentioned in her journal. Part of this operation would consist of testing Cyclo-synthetic neural transmission gene sequences. Modification of these sequences would allow for increased intelligence and conginitive capabilities. This procedure was one of several proposed augmentations for the SPARTAN-II Program, but was rejected due to high rates of psychotic and anti-social behavior. Operation: TENDRIL was to look into long term effects of the procedure applied to young candidates over an extensive period of time.