Since Sept. 11, 2001, the department has spent millions of dollars on high-tech equipment to detect and deter biological, radiological and nuclear threats.

Some of these gadgets, like the handheld devices that police use for bag inspections in the subways to detect bomb-making materials, have become as ubiquitous to New Yorkers as roasted peanut carts.

Others, like the department's remote-controlled underwater robots, or ROVs (Remotely Operated Vehicles), are a bit more inconspicuous.

The ROVs resemble mini submarines with dual propellers, wide-angle lenses and halogen lamps. Once submerged to depths of up to 200 feet, they beam up live color video through an umbilical cord to a 17-inch screen. Separate sonar images appear on a laptop computer.

The AP's TOM HAYS recently saw one of them in action when he went out with the department's scuba unit to inspect a busy Manhattan heliport where the president's helicopter, Marine One, sometimes lands.

For the scuba unit, it's become part of their daily routine.

"There's miles and miles of coastline involved here, and obviously they can't be everywhere at once, but they do have a long list of what they believe to be sensitive sites -- potential targets," Hays says. "Pretty much every day they're out examining at least two or three of those ... even when there's no hard evidence or intelligence that they should be looking for something.

"They want to get out there pre-emptively."

In this video report, asap talks to Hays about what learned and saw during his outing.

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Watch the video here: http://asap.ap.org/data/interactives/_news/underwater/

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Jaime Holguin is an asap reporter based in New York.

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