HONOLULU (AP) — A live mortar round was found in a vehicle at a gate to the sprawling Pearl Harbor military base, shutting down the base for hours and leading three people to be taken into custody, military officials said Wednesday.

It’s not clear what the trio planned to do or where they wanted to go when they were stopped late Tuesday, base spokesman Charles Anthony said, calling the mortar round “an explosive device” and “a deadly weapon.”

A mortar is a portable weapon that is loaded and fired by dropping an exploding shell into a tube. Anthony said no firing device was in the car. He said the round could be modified and triggered by something other than a traditional mortar tube, but no detonation system was found in the vehicle.

Hundreds of people, usually lost, end up at the Pearl Harbor gate daily and are turned around if they don’t have proper identification to enter, Anthony said.

“The security guard first noticed the smell of marijuana and then looked inside the vehicle and saw what was potential ordnance,” he said.

Joint Base Pearl Harbor-Hickam was shut down about 10:30 p.m. Tuesday to incoming and outgoing traffic while a bomb squad investigated the vehicle that appeared without authorization to enter, the Navy said in a statement.

The base’s gates were closed for about two hours. There were no injuries.

Naval Criminal Investigative Service is investigating and took custody of the three suspects, Anthony said.

The base is home to a naval shipyard where an active-duty U.S. sailor opened fire on three civilian employees in December, killing two of them. Officials have said the sailor, whose submarine was docked at Pearl Harbor, then took his own life.

The shooting happened days before dignitaries and veterans attended the base’s ceremony to mark the 78th anniversary of the Japanese attack on Pearl Harbor.