The B-52 bomber ground-attack exercise occurred over O'ahu for several days at the end of February.

If the presence of the Cold War-era eight-engine jets wasn't apparent, that's because they were at 20,000 to 25,000 feet, and never touched down in Hawai'i during the drill, which takes place every quarter.

O'ahu provides good urban training practice for the bombers, which are deployed to Guam and are part of a continuing force buildup on the U.S. territory far across the Pacific.

"We definitely don't want to drop down low to disturb the public," said Maj. Brian Bogue, who works in bomber and contingency operations for the 13th Air Force. "And honestly nowadays, pretty much wars are fought at high level (for bombers), so it's very realistic for us to stay that high."

The "Koa Lightning" exercise Feb. 26 to 28 also was a chance to provide intercept and air defense training for Hawai'i Air National Guard F-15s.

But it also served as a scouting mission over 109,000-acre Pohakuloa Training Area on the Big Island as part of a plan to drop inert bombs there — something the Air Force now can't do with B-52s.

Now, a target has to be positively, or visually, acquired.

"That's never going to happen with a bomber," Bogue said. "With a fighter they can roll in and see the target. Then they can release their weapons."

The Air Force is working on changing regulations so nonexplosive ordnance can be dropped by B-52s at Pohakuloa.

The B-52, which first flew in 1954, began as an intercontinental high-altitude nuclear bomber. According to the Web site globalsecurity.org, 94 B-52Hs are all that remain of 744 Stratofortresses built in the 1950s and 1960s.

But the aircraft continues to be extremely versatile, and in 2004 off Kaua'i, the B-52 again made history by sinking moving ships at sea with satellite-guided 2,000-pound bombs.

Six Stratofortresses are deployed to Guam. Regular rotations began more than two years ago, with the U.S. saying the presence serves as a "prudent deterrent capability" — a warning largely directed at North Korea, with so many U.S. forces committed in Iraq and Afghanistan.

B-2 stealth bombers also have deployed to Guam, 8,300 Marines are being moved there from Japan, and several nuclear attack submarines are being based there.

B-52s flying out of Guam last month dropped inert mines over the Mariana Trench from 1,000 feet — a job usually performed by ships. The B-52 can drop 12 satellite-guided "smart bombs," the Air Force said.

For the February exercise over Hawai'i, four B-52s made the approximately 18-hour round trip from Guam, getting refueled along the way and working with ground controllers on O'ahu from the 25th Air Support Operations Squadron.

"The B-52 really has adapted well, and the Air Force has kept up well in the current missions out there," Bogue said. "It will play a huge role ... in any type of conflict that we might have but we'd like to avoid, obviously."

Reach William Cole at wcole@honoluluadvertiser.com.