NORTH CHARLESTON — As records go, this one was a whopper.

Twenty huge C-17 transport planes took off Thursday from Charleston Air Force Base and flew in a 6½-mile-long formation over the Arthur Ravenel Bridge.

Then, they hung a left and took a 20-minute trip to North Field in Orangeburg County. There, each dropped a 2,000-pound, parachute-equipped pallet and then headed home.

The formation of 20 C-17s, each large enough to hold the contents of four 18-wheel trucks, was the largest ever launched from one base at one time in Air Force history. The feat broke the previous mark of 17 set a year ago by Charleston crews.

“Everything looked real good,” said Col. Steve Harrison, vice commander of the Charleston-based 437th Airlift Wing, a passenger on the second plane in the formation.

Aboard Harrison’s plane, airmen posed for pictures to record their role in the event. As the formation approached the Ravenel Bridge, the crew lowered the plane’s back door, giving passengers a spectacular 10-foot-by-18-foot window to view the planes that followed.

The transports, which have 54-foot-high tails and 170-foot wingspans, were spaced 2,000 feet apart, following each other as if they were on a rope. Their high-wing design made it look like they were suspended in air as they cruised 2,000 feet above the bridge.

While records are nice, Thursday’s event provided needed training for the airmen, said Harrison, who flew in a 15-plane formation three years ago when he was a C-17 pilot at McChord Air Force Base, Wash.

Learning to fly in large formations helps C-17 crews meet the Army’s goal of quickly airdropping a brigade of troops and equipment into enemy territory. A brigade has about 3,250 soldiers and 3,450 tons of equipment.

The airdrop exercise also prepared crews for future assignments in places like Afghanistan. There, C-17s have taken over the role of resupplying troops at bases that are difficult to reach by truck convoys.

Pilot Capt. Todd Markwart of Phoenix and his crew had nine seconds Thursday to drop their payload over a target area 1,700 yards long and 1,100 yards wide.

“In Afghanistan, the drop zones are more austere and remote,” Markwart said. “You might have a drop zone that’s only 100 yards by 100 yards on top of a mountain clearing.”

After finishing the exercise, nine planes peeled off from the formation to rendezvous with tankers and refuel over the Atlantic Ocean, about 60 miles northeast of Charleston. The remaining 11 planes returned directly to the Charleston air base.

Crews from the 437th, the active-duty unit at Charleston, and the 315th Airlift Wing Reserve flew in the exercise.

On an average day, the base launches about 10 planes, Harrison said. Usually, five take off in the morning, the remainder later in the day.

Overall, 53 C-17s are assigned to Charleston. On average, the base’s planes move 295 tons of cargo daily.

About 45 percent of all air cargo bound for U.S. troops in Iraq and Afghanistan is flown out of Charleston.

Reach Crumbo at (803) 771-8503.