CAMP PENDLETON, Calif. (AP) — Brig. Gen. Rex McMillian watched proudly Friday from a scrubby bluff as hundreds of Marines in seafaring tanks hit the Southern California beach in perfect unison with support helicopters buzzing overhead.

It had been nearly 10 years since his Marines last trained in such a large-scale beach invasion exercise with the Navy.

With the wars in Afghanistan and Iraq taking troops to landlocked regions, many of the Marines had never been on a ship — let alone stormed a beach — until the "Dawn Blitz" exercise, the largest of its kind on the West Coast since the Sept. 11 terror attacks. The two-week training drill ended with 5,000 Marines and sailors staging the mock invasion.

The exercise came two days before the D-Day anniversary and at a pivotal time for the Marines as they face questions from Defense Secretary Robert Gates about whether major amphibious landings that made the Corps so famous worldwide are becoming outdated in today's warfare.

As the sun streamed through dissipating morning clouds, the troops landed at exactly 9:15 a.m. as planned — 45 minutes after leaving the cavernous interior of the USS Bonhomme Richard about 20 miles off the coast of Camp Pendleton.

Seconds after rolling in with the deep-blue waves, the Marines poured from their tanks and took their positions, keeping low and aiming their assault rifles toward their imaginary enemy.

California's morning freeway traffic flowed by on the horizon, with drivers unaware of the drill that Marines said was crucial to maintaining their skills as a versatile force for combat missions and humanitarian operations.

"I think they executed this superbly," McMillian said, smiling.

On Sunday, Americans honor the heroes of D-Day on the 66th anniversary of the June 6, 1944 invasion of Normandy, the largest amphibious landing ever that was credited with turning around WWII.

"The lessons we've learned 60 years ago, we've kind of encoded them into our genetics," Marine Maj. Howard Hall said as he stood in front of a bank of radios at a command center aboard the Bonhomme Richard, an 844-foot-long assault ship.

Gates has questioned the modern value of such operations and equipment at a time when enemy anti-ship technology has become increasingly sophisticated, making beach invasions much more difficult.

Gates is scrutinizing every aspect of the military in his search for roughly $10 billion in annual savings.

He has expressed doubts about a $13.2 billion plan to buy large numbers of the amphibious Expeditionary Fighting Vehicle for the Marine Corps starting in 2012. The vehicles, also known as EFVs, help get troops from ship to shore while under fire and mark a significant upgrade over current technology.

With relations between the Koreas deteriorating since 46 sailors were killed in March during the sinking of a South Korean ship, defense analysts warn that Gates should not to be shortsighted, and that future conflicts are likely to be in coastal countries.

Lt. Gen. Joe Dunford said the Marine Corps intended to stage other large-scale landing exercises every other year now that deployments to Iraq and Afghanistan are expected to ease.

"What we're doing today is relevant across the spectrum," Dunford said.

Australian Army Lt. Col. Jake Ellwood observed "Dawn Blitz" to see what lessons he could take back to his country, which recently purchased two amphibious assault ships

The storming of the California beach reinvigorated Marines such as Lance Cpl. Grant Ayres, 24, who peeked from the hatch of his tank after he hit the beach and watched the next wave of troops ride the surf to the beach.

"Now I have a little bit more of a picture in my mind so I'm more prepared," said Ayres, kneeling on the sand in front of his amphibious assault vehicle, pointing his rifle out to the Pacific. "I'll know next time what's going on outside when I'm in one of these as we head into the unknown."

After three years in the Marines, the past two weeks marked the first time Ayres had slept on a ship. He has served one tour in Iraq.

"I didn't take sea sickness pills on the ship," he said proudly. "But I did get lost moving around the ship with all the ladders and passageways."

(This version CORRECTS RECASTS. corrects style on Lance Cpl. Minor edits.)