The U.S. military is considering investing more than $211 million into construction in Darwin, Australia, according to the Senate’s version of the annual defense legislation.

What that money will build is unknown. The Marine and Navy officials Marine Corps Times reached out to have yet to provide a statement.

Australian outlet ABC News reported that secret planning is underway to develop a new commercial port just outside of Darwin that could eventually be developed to house Australia’s landing helicopter dock ships or the U.S. amphibious assault ships that ferry Marines around the globe.

While Australia is one of America’s most important military allies in the Pacific, the military construction could cause diplomatic headaches for Australia and sour its relationship with China, which over the years has become more economically intertwined.

“Because just like even our best allies, the Australians, they’re with us from a military perspective, but economically they’re tied to China," Maj. Gen. Daniel Yoo, the commander of the Marine Raiders, told Marine Corps Times in an interview during a May special operations conference in Tampa, Florida.

“And so they have a problem internal to their own country as far as there’s some that feel they should be closer to China, because their economic health is dependent upon it."

It’s a strategic tightrope act the U.S. military has to walk in the Pacific where China’s economic might is changing the U.S. military calculus in the region.

Marines deploy to Australia every year to conduct training with Pacific allies in the region. Marine officials have told Marine Corps Times there are no plans for a permanent Marine presence.

But, there are nearly 1,700 Marines in Australia taking part in training exercises across the Pacific country — it’s the largest rotation to date and includes the most robust aviation element thus far.

The Corps slowly has been increasing its footprint in Australia over the past eight rotation cycles. In 2018, nearly 1,500 Marines took part in exercises across Australia; the goal is to bump that number to 2,500 Marines.

Australia is important to America’s strategy in the Pacific and to the Corps’ plans to move some of its forces off of Okinawa, Japan.

While the Corps doesn’t have a permanent presence in Australia, a major U.S. military construction project near Darwin is likely to irk China and complicate delicate efforts by Australian officials to balance its relationship with both heavyweights.

“As economic power shifts, it’s unsurprising that nations will seek to play a bigger strategic role in our region. China, in particular, is exercising unprecedented influence in the Indo-Pacific,” Australian Prime Minister Scott Morrison said in a November 2018 speech.

Once more steadfast allies are now having to consider their economic future with China and their traditional military and democratic partnership with America.

“Australia also has a vitally important relationship with China. Trade, tourism and educational exchanges are at record highs,” Morrison said in his speech.

“Of course, China is not alone in being a force of change in our world. But China is the country that is most changing the balance of power, sometimes in ways that challenge important U.S. interests,” Morrison said.

“Inevitably, in the period ahead, we will be navigating a higher degree of US-China strategic competition."

Congress may review the Corps’ plan to redistribute its forces across the Pacific.

The Corps kicked off a portion of the Talisman Sabre exercise in Australia around mid-July where Marines, Army and Australian forces carried out a HIMARS rocket artillery raid and captured an airfield.