OKINAWA, Japan — Marines ­forward deployed here to this Pacific island don’t have much time to enjoy the beaches, coral reefs and world-class scuba diving.

In fact, some Marines stationed here say they spend very little time on the island at all, as a relentless operational tempo is forcing the III Marine Expeditionary Force to routinely deploy forces up and down the Pacific rim.

“I call it the gerbil wheel,” Col. Tye Wallace, commanding officer of the 31st Marine Expeditionary Unit, said in a ­recent interview at III MEF headquarters at Camp Courtney, Okinawa.

“It has a high operational tempo to learn and practice in your trade as a Marine.”

“If you want to get good fast, there’s an opportunity,” he said.

A decade ago, Okinawa offered Marines a break from the grueling deployment cycles that was the norm for grunts at Camp Lejeune and Camp Pendleton who were constantly deploying to Iraq and Afghanistan.

Now, however, those Middle East deployments are rare. And in Asia, hot spots like North Korea and the region’s intense geopolitical rivalries are demanding frequent and far-flung deployments for III MEF and its forces that are based in Okinawa, Hawaii, Iwakuni, Japan, and Darwin, Australia.

There’s been an “explosion in off-island deployments and training opportunities for Okinawa-based units,” said Col. Scott Fosdal, operations officer of 3rd Marine Division, the ground component of III MEF, who is on his third Okinawa tour.

The most significant new threat in the region is likely North Korea’s rapidly advancing missile threat, said Carl Baker, an Asia expert at the Center for Strategic and International Studies.

If North Korea were to invade South Korea, the 31st MEU would likely be among the first American units called to the fight.

Meanwhile, the growth of China’s military is also fueling the U.S. Marines’ operational tempo in Asia, specifically in the East China Sea and South China Sea.

“China’s growing naval capabilities and expanded Coast Guard fleet are more significant than 10 years ago,” Baker said.

Containing China is prompting the ­Marines to conduct frequent security ­cooperation missions with countries like Singapore, Malaysia, Vietnam and Indonesia.

Another flashpoint with China could be the uninhabited Senkaku islands in the East China Sea, which are ­controlled by Japan but also claimed by China, Baker said.

Marines from Okinawa routinely work alongside the Japanese military, known as the Self-Defense Forces, to prepare for amphibious warfare in the event the Chinese invade those islands, Baker has said.

Marines are also returning to the Philippines as the rocky U.S. ­alliance there gets back on track. The ­controversial Filipino president, ­Rodrigo Duterte, had called former U.S. President Barack Obama a “son of a whore” and told U.S. special operations forces to leave the country.

Yet in early October, Filipino troops and Marines with the 3rd Marine Expeditionary Brigade participated in a new counterterrorism and ­disaster-response exercise in the Philippines called Kamandag, which is “emphasizing the close partnership between the ­Philippines and United States militaries,” according to a news release by the U.S. embassy in Manila.

With all of those countries demanding the U.S. military’s attention, Marines from III MEF could be in up to 20 countries across the Pacific Command region on a given day, Marines said.

In the coming year, the 3rd Marine Division has 70 exercises and mission rehearsals, Fosdal said, ranging from the employment of just one platoon to a full battalion. The division has major deployments to the Philippines, Korea, Guam, Thailand and around the Japanese mainland, he said.

The mix of missions in Asia imposes a unique deployment cycle on the Marines with the 31st MEU. Unlike the Corps’ other six MEUs based in the United States, the forward-deployed 31st MEU’s deployments are far shorter and far more frequent than the typical six- or ­seven-month floats.

And aside from Australia-based forces in Darwin, each infantry battalion and artillery battery will spend three to four months deployed off Okinawa in some way.

“On any given day, in addition to ­Okinawa and Hawaii, we have division forces in the Philippines, Camp Fuji and usually Korea,” Fosdal said.

“Moving Marines and equipment from country to country via a combination of air and surface connectors stresses a unit’s staff planning and execution like no CONUS training can,” he said.

It is not that unusual for a battalion staff to break up into multiple command groups that each deploy to different countries.

“For example, one battalion just had a rifle company reinforced with Light Armored Reconnaissance, Force Recon and Marine Logistics Group attachments training with a Japanese Army Brigade in Hokkaido while simultaneously employing its Alpha command and a rifle company reinforced in Korea with a ROK Marine battalion,” he said.

“All while the battalion’s third rifle company deployed … in Singapore and Indonesia.”

That battalion eventually reunited most of its forces in South Korea, then returned to Okinawa, he said.

Andrea Scott is managing editor of Marine Corps Times. On Twitter: @_andreascott.