U.S. and Australian troops have been fighting together since World War I, but President Trump's recent spat with Australia's prime minister underscores that cooperation between the two countries has not always been easy.

Since 2012, the U.S. has rotated a small force of Marines through Darwin, Australia. Both countries had hoped to send a full Marine Air-Ground Task Force of 2,500 Marines to Australia by 2016, but that timeline has been pushed back to around 2020.

The plan fell behind schedule amid negotiations between the two countries about who should pay to build the infrastructure for the extra Marines, said Andrew Shearer, a former Australian defense official.

"There was quite a long delay — 18 or 20 months — to conclude a cost-sharing agreement," said Shearer, with the Center for Strategic and International Studies think tank. "Those cost-sharing negotiations, which were difficult — and I think a little bit acrimonious at officials' level — that was concluded last October."

In addition to disagreements about money, some U.S. officials felt the cost-share arrangement should mirror arrangements with other allies, such as South Korea and Japan; while Australian officials objected to applying a "cookie cutter model" to their country, he said.

"Even close allies have pretty tough negotiations with each other over this sort of burden-sharing," Shearer said. "I think negotiations just got off to a slightly bad start. I think that, frankly, there wasn't enough political push from both sides to get their officials to get the thing over the line sooner."

Movement to Contact

U.S. Marines with 1st Battalion, 1st Marine Regiment, conduct a movement to contact drill at Bradshaw Field Training Area, Northern Territory, Australia, Aug. 10, 2016.

Currently, both countries are assessing how much construction is needed at Robertson Army Barracks in Darwin and Royal Australian Air Force Base Darwin, Shearer said.

"Now they're up to where — in my view, frankly — they should have been 12 or 18 months ago," he said.

The special relationship between the U.S. and Australia was tested again on Tuesday when Trump reportedly had an angry phone call with Australian Prime Minister Malcolm Turnbull about an agreement made under the Obama administration for the U.S. to accept 1,250 refugees being held in Australia's offshore detention centers. Trump hung up on Turnbull after 25 minutes, according to the Washington Post.

No changes have been made to the planned rotations of Marines to Australia since the two leaders spoke, said Maj. Rob Shuford, a spokesman for U.S. Pacific Command.

"The U.S. alliance with Australia remains an anchor of peace and stability in the region and our mil-to-mil relationship remains solid," Shuford told Marine Corps Times on Thursday.

Australia is a key ally and was a major part of the Obama administration's effort on the Asia-Pacific region. But the so-called  "pivot to Asia" ended up being more symbolic than substance as threats in the Middle East re-emerged.

The latest rotation to Darwin begins in April and will involve 1,250 Marines, mostly from 3rd Battalion, 4th Marines, based at Camp Pendleton, California, said Chuck Little, a spokesman for U.S. Marine Corps Forces, Pacific.

The Marines are also sending the most aircraft to Australia since the rotations there started, Little said. The aviation combat element will be made up of four MV-22B Ospreys from Marine Medium Tiltrotor Squadron 268; along with five AH-1W Super Cobra and four UH-1Y Venom helicopters from Marine Light Attack Helicopter Squadron 367. Both squadrons are based at Marine Corps Air Station Kaneohe Bay, Hawaii.

Little confirmed that the U.S. and Australia are reviewing how much infrastructure needs to be added to Robertson Army Barracks and RAAF Darwin to accommodate 2,500 Marines and their aircraft.

There is no set time line yet for when an entire Marine Air-Ground Task Force will rotate through Australia, he said.

"We continue to work with our Australian counterparts on the best way forward with our rotational deployments to Darwin to include the size of the force and its composition," Little said.