Carter has devoted more personal attention to his Indian counterpart than any other, and that groundwork could prove crucial as the Obama administration prepares to hand over the reins with questions looming about President-elect Donald Trump's commitment to its pivot to Asia and how confrontational he will be with Beijing.
The US-India relationship has been ascendant for many years and intensified under President Barack Obama as his Asian strategy sought to balance the rise of China, but the state of the alliance remains mixed at best. The US only recently made small inroads into the Indian defense markets and historical skepticism within India at the prospect of more robust relations with America persists.
But en route to New Delhi, Carter told reporters, "India and the United States are destined to be strategic partners."
The relationship has "grown by leaps and bounds" since 2008, Carter said, adding that he intended to discuss with his counterpart a "major change" that is "very close to the finish line" regarding the easing of regulations on defense exports to India.
"It permits us to do things with India that have never been possible before" by creating a "presumption of approval for transactions with India," he added.
Carter and his Indian counterpart, Defense Minister Manohar Parrikar, were due to hold their seventh meeting Thursday, and Carter has previously said he has spent more time with him than "any other defense counterpart anywhere in the world."
The two men are said to have a lot in common, both rising to their respective nation's top defense posts while possessing backgrounds in science and engineering.
"They have a very strong personal relationship," a senior defense official told CNN, crediting Carter with being the leading force behind Obama's effort to bolster US-India ties.
"Ash Carter is the champion of this relationship in the administration," the official said.
But some observers of US-India relations noted that the improved bilateral defense relationship predates both Carter and Obama.
"I think the US- India defense relationship has blossomed over the years irrespective of Obama's 'pivot/rebalance to Asia' policy," Bharath Gopalaswamy, director of the South Asia Center at the Washington-based Atlantic Council, told CNN.
He said that "the security relationship between the two countries have slowly remained on the upward trajectory" ever since the US and India signed an accord governing civil nuclear issues during the George W. Bush administration.
In recent months, the US and India have signed several more accords, including a logistics exchange memorandum of agreement that will allow the US and Indian navies to receive logistical support at each other's installations.
Carter has also trumpeted increased joint military exercises between the two nations and has highlighted how the Asian pivot has coincided with Indian Prime Minister Narendra Modi's "Act East Policy," a diplomatic initiative aimed at boosting India's presence and relationships in East and Southeast Asia.
Carter said Wednesday that he was encouraging India to increase the pace of joint military exercises both with the US and American allies.
Some analysts in Washington and New Delhi see the two large democracies as natural allies, particularly given China's increasingly assertive actions in the region, such as the construction of islands equipped with military-capable runways.
"As the world's two largest democracies, we are uniquely poised to help bring greater security and prosperity to the entire region," Adm. Harry Harris, commander of US forces in the Pacific, told Congress in February.
While neither country explicitly names China as a reason for their pursuit of enhanced collaboration, officials from both countries have underscored the need for "rule-based order" in the Indian and Pacific Oceans.
China has been accused of violating such rules via its aggressive island-building programs in the South China Sea and its claims to large areas of that critical body of water. India and China also share a land border that continues to be disputed decades after the two nations fought a border war.
Upon landing in New Delhi, Carter told reporters that China's actions had alienated countries in the region and said the US must maintain a military capability advantage over China while seeking cooperation where possible.
Tighter US-India coordination on military affairs is a significant departure from the past. During the Cold War, India avoided any such cooperation as part of its membership in the movement of non-aligned countries.
But that has been changing in recent years, especially once Modi was elected in 2014. During his visit to Washington in June, the US designated India a "major defense partner."
But Parrikar himself has acknowledged the challenges involved in boosting the two countries' military cooperation, noting that mistrust and skepticism among the Indian public had challenged even the signing of the logistics agreement, with people falsely believing that it would lead to US bases in India.
India's complicated history with the US is also reflected in its purchase or arms. While the US government and American defense firms would welcome the chance to sell more weapons and equipment to India, for decades New Delhi has traditionally bought its arms from Russia and before that the Soviet Union.
"We come from a history of separateness," Carter acknowledged.
India is the world's biggest importer of arms, receiving 14% of all global deliveries from 2011-2015, according to statistics compiled by the Stockholm International Peace Research Institute, or SIPRI.
Its biggest supplier is Russia, which provided 70% of those arms transfers, while the US lags behind in second place, responsible for only 14% of Indian imports. And in 2012, the US lost out on a major competition for India's fighter jet to the French.
But the US has also enjoyed some successes under the Obama administration, with the Indian military opting to purchase C-130J transport planes from US-based Lockheed Martin -- a deal the company described as representing "the first major military contract between the US and India in more than 40 years."
Last week, the Indian government signed a long-awaited contract on artillery pieces with BAE Systems North America valued at close to $750 million.
"We've made significant progress on the defense side with India," the defense official said. US arms exports to India were 11 times higher in 2010-2015 than 2006-2010, according to SIPRI.
Further complicating the burgeoning US-India relationship was Trump's recent call with the leader of India's long-time adversary, Pakistan President Nawaz Sharif.
A transcript of that call issued by the Pakistani Foreign Ministry depicted Trump complimenting Sharif.
"I think the Indian administration, like many other administrations, share a sense of nervousness about the Trump administration," Gopalaswamy of the Atlantic Council said.
But Gopalaswamy was skeptical that the call with the Pakistani premier would have a demonstrable effect, saying, "Concerns about the transcript posing any challenges to US-India defense relationship are overstated."