The Delaware National Guard increased security Wednesday at an air base after different vehicles approached its gate this week, then left.
In at least some of the five incidents at the New Castle Air National Guard Base near Wilmington, an individual asked for directions, said Col. Len Gratteri, a base spokesman. In at least one case, a vehicle turned around before reaching the main gate.
It's not uncommon for people to get lost and ask for directions, Gratteri said. It was the frequency that prompted heightened security.
"That's the activity we think is suspicious. ... Is it a coincidence, or is it a part of something else?" he said.
Gratteri said he does not believe the same vehicle or same individuals were involved each time. Investigators are reviewing security camera footage.
Vice President Joe Biden, who is from Delaware, has flown to the airport in the past on Air Force Two.
Officials of the base's 166th Airlift Wing of the Delaware National Guard posted a message Tuesday on their website, instructing personnel on how to spot and report suspicious activity. It detailed categories of suspicious behavior, including surveillance and attempts to test security or gain access to a base.