Even more pedantic point, ARGUS probably has a 4th role as filled by her predecessor. RFA ENGADINES war-role was only recently declassified, but she was to have acted as the base ship for a continuity of govt party. Its likely Argus would have done something similar - the plans were TS Codeword though, so highly unlikely that anyone who served onboard would have known anything about this.
She had a major refit a couple of years ago that reduced her flight spots from 5 to 3 and binned an aircraft lift to make way for an improved access / exit / escape and triage area for the hospital. And operationally, if the hospital is needed, flying training gets fcuked off. This observer (not the WAFU kind) suggests that the primary role is as PCRF as angrydoc says.