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From its Lower Manhattan headquarters three blocks north of Wall Street, an unlikely city agency seemed to be ramping up for battle.

It bought 140 Glock 9-millimeter semiautomatic pistols. It spent $155,000 on ammunition, $140,000 on body armor, more than $800,000 on two-way radios and $54,000 for night-vision goggles. There were discussions about buying assault rifles and even acquiring a decommissioned police boat.

Such an approach might be standard procedure for a front-line law enforcement agency like the Police Department, but it wasn’t exactly typical for the city’s Department of Investigation.

The agency is charged with investigating waste, corruption and mismanagement in city government, where it has traditionally focused, in large measure, on white-collar crime. None of its employees have been shot at or assaulted in the line of duty, according to the agency, and officials could not recall a single instance in which an employee had fired a gun at a crime suspect.