TULSA, Oklahoma - Attack helicopters have become a common sight in the skies over Tulsa, as U.S. Army and Army National Guard units head west for annual training.

Many of the aircraft belong to the 1-135th Attack Reconnaissance Battalion based at Whiteman Air Force Base, located about an hour east of Kansas City.

The helicopters are Boeing AH-64D Apaches. They're two-seaters, with a pilot in the back seat and a co-pilot/gunner in the front.

They're very different from the Black Hawk transport helicopters based near Tulsa International Airport.

According to Major John Martin, Acting Administrative Officer for the 35th Combat Aviation Brigade, the choppers are heading to Boise, Idaho where they'll use a gunnery range to sharpen their skills.

It's a four-day trip that requires frequent stops for fuel, with Tulsa being the first one. The crews are avoiding the bad weather in the Rocky Mountains, so they loop around to the south which brings them right to Tulsa.

"We love to stop in Tulsa for fuel," said Major Martin.

The Apaches can be an impressive sight during the trip, because they usually fly in groups of four or five. Major Martin says they fly together in case one has a problem.

They get about two and a half hours of flight on a tank of gas, so that means three stops a day on the trip.

"It's like driving in a car, you're ready to be done for the day and get out," Major Martin said.

Some of the Apaches seen over Tulsa this week are probably from other units heading to the same gunnery range.

Major Martin says Apaches from the Whiteman unit will be flying over Tulsa again on the way back home in 25 to 30 days.