LOS ANGELES (CBSLA.com) — For the first time, a news crew has been allowed to fly in a helicopter that circles the city’s incoming cargo ships, scanning for illegal radioactive material that could be smuggled in by sea.

It’s a fear that’s heightened as North Korea pushes on with its nuclear testing, posing a serious security threat to the U.S.

A video that recently surfaced from North Korea state-run media showed a screening of what appeared to be a fictional nuclear annihilation of San Francisco. And adding yet more uncertainty: the future of the U.S. nuclear deal with Iran.

Of all the ports in the country, Los Angeles is the busiest, putting it at real risk.

The L.A. County Sheriff’s Department Special Enforcement Bureau has the critical duty of protecting the port from an ultimate threat.

“I think the most plausible would be a nuclear device that snuck in, a dirty bomb basically,” says LASD Sgt. Eric Fox.

The elite group invited CBS2’s Jennifer Kastner on board for a rare look at their work, doing both random and targeted screening of ship coming into L.A. and Long Beach.

An underwater robot looks for unusual types of radiation, while a high-speed boat known as the Raptor is used for inspections.

One recent video from the Sheriff’s Department during a recent operation showed authorities boarding one of the incoming cargo ships to do a full sweep.

Officers have the only chemical and biological detection dog in the country: Johnny Ringo.

“He’s trained to detect ricin. Anthrax, nerve agents, blister agents,” LASD detective Wayne Carpini said.

And when the need arises for further investigation, Air Rescue 5 takes off to hover above the vessels and uses aerial radiation detection devices to find out what’s below.

It’s a little known sector of local law enforcement tasked with a big responsibility.

“We do the best job we can to protect our nation, all hours of the day and night,” said SWAT Lt. Thomas Giandomenico.