In
Larry Niven's
Known Space future history, ARM means the
Amalgamated Regional
Militia, essentially the
United Nations police. It is also slang for a member of the organization.
Gil Hamilton is an example of the earlier ARM. Although they lose power, even at the late end of Known Space (the
Ringworld trilogy) the ARM is still a force to reckon with.
One of the techniques used by the ARM is situational insanity. Many of their agents are paranoids and psychotics. They are treated for their insanity, but while at work, their treatment is withheld, allowing the ARM to have an extra edge, a measure of creativity denied to most organizations. This use of controlled madness saves humanity's collective bacon more than once in the series.