The V-22 Osprey shudders as it approaches the landing zone and its two massive propellors shift from forward-facing for conventional flight to the vertical position, enabling the aircraft to hover and touch down like a helicopter.

This aircraft is just one way in which the US Marine Corps will go into combat should the necessity arise in the Indo-Pacific region.

Camp Gonsalves covers more than 35 square kilometers of jungle in the far northeast of Okinawa's main island and is home to the US Marine Corps' Jungle Warfare Training Center, widely considered as the most challenging facility of its kind in the world.

The base and its team of dedicated trainers are in great demand among other branches of the US military as well as its allies. Units from Japan are regularly put through their paces in this unforgiving environment, along with detachments of British and Dutch troops in the last year alone.

Changing geopolitical environment

Japan, the US and their partners are aware that the security situation in the Indo-Pacific has changed dramatically in the last decade.

Although senior officers are reluctant to single out any individual nation as the cause for deepening concern about the growing possibility of conflict, it is quite clear that a shift in defense postures and strategies, combined with stepped-up training and other preparations, are aimed at China as a potential adversary.

"We prepare here for a future fight against a peer adversary," a Marine Corps officer overseeing training at the facility told DW. "Our job is to train people in jungle operations so they are prepared to fight and win in this kind of environment," said the officer, who cannot be named for operational reasons.

"The jungles and mountains of Okinawa are some of the most challenging environments to work and fight in and we feel that anyone who has gone through the training here will be able to work in the most challenging environments in the world, including South America, Africa and Southeast Asia," the officer said.

Much of the Indo-Pacific region includes jungle environments, including the Philippines, Malaysia and Vietnam, all of which are involved in disputes with Beijing over territory in the South China Sea.

This list also includes Taiwan, which China insists should be subsumed into the mainland and is the target of growing military and political pressure.

Transitioning from desert to jungle

Initially set up as a guerilla training school in 1957, Camp Gonsalves later became the focus of US forces' jungle warfare training. By the turn of the century, however, the US had shifted much of its focus to preparing to operate in the desert and mountain terrains of the Middle East and Afghanistan.

"We had become very good at fighting in desert environments, but it was recognized that we needed to look at other areas where we needed to be better, such as arctic, jungle and other potential operating environments," the training officer said. "We had no idea where that might be, but we did know that we needed to be ready."

As a consequence, training here is being ramped up once more. In 2022, some 14,000 US and allied troops completed courses at Camp Gonsalves. By the end of this year, more than 16,000 troops will have trained here over the previous 12 months.

The base operates a series of courses, including a grueling five-week jungle leader program, a jungle survival and small-unit leadership scheme and the 12-day jungle medicine course, which focuses on prolonged casualty care in this unforgiving environment as well as instruction on live blood transfusions and treating snake bites.

Challenging training environment

Camp Gonsalves occupies a hill in the center of the training area, with five separate areas providing different terrain and challenges. One has a recreation of a civilian village, others have water features that need to be negotiated, while the area where the jungle meets the Pacific Ocean is used for open-water survival drills and unit insertions and extractions.

Asked which of the areas is the most taxing, the instructor immediately points out the northernmost area, which is traversed by a range of steep mountains and can be "challenging in terms of mobility and sustainability" due to the high temperatures and humidity common in the area in the summer months.

One exercise requires units to cross this mountain range and two rivers over a period of 48 hours, the officer said, adding that anyone taking part will be "wet the entire time, either from sweat, rain or the rivers."

Another key element of this remote facility is the 6-kilometer training course, which commences with troops rappelling down a sheer 20-meter rock face. Operating in units, soldiers must also overcome a series of water obstacles and other physical challenges before they finally reach the final test of their stamina, a place the instructors refer to as "the pit."

Two marines slip beneath razor wire entanglements and into a pool of murky water that comes up their chins. An instructor has a long, hooked pole to hand and is keeping a close watch for poisonous "habu" snakes that thrive in this environment.

The marines negotiate the pool and enter a waterlogged trench at the far end, crawling beneath the overhanging foliage and working in tandem to pass beneath more razor wire.

They are next required to enter a large, enclosed water tank and pull themselves along the underside of the roof until they emerge at the far end. After that, it's back into more trenches and beneath more barbed wire and log obstacles until they emerge, coated in mud and water slime, but grinning.

Editor's Note: The reporter was among a press team invited by the US military to visit US military installations in Okinawa.

Edited by: Wesley Rahn