US Defence Secretary Leon Panetta will travel on Sunday to Vietnam's Cam Ranh Bay, a major base for American forces in the Vietnam War, underscoring improved ties between the former enemies.
Panetta is the most high-ranking US official to visit Cam Ranh Bay since the end of the Vietnam War in 1975.
The two countries signed a memorandum on defence cooperation last year and Panetta planned to discuss how to carry out the agreement during his two-day visit, officials said.
"We've had a great trajectory with Vietnam over a number of years," said a senior US defence official, who spoke on condition of anonymity.
"Seventeen years into normalisation of relations, we really have a robust relationship with the Vietnamese government as a whole and our mil-to-mil (military) relationship is really healthy as well," the official said.
Cam Ranh Bay airfield, one of three main hubs used by US forces in the war, once hosted squadrons of fighter jets, cargo planes and troops at the height of the Vietnam conflict.
The Vietnamese handed over the air base and naval port to the Soviet Union after the war, with Moscow deploying fighter jets, nuclear submarines and a spy station during the Cold War.
The Russians left the base in 2002 and Vietnam has decided to open the port on a commercial basis to foreign naval ships to resupply and undergo repair work.
Panetta was due to visit an American naval cargo ship currently at the port, the USNS Richard E. Byrd, which moves cargo for the naval fleet with a mostly civilian crew, officials said.
The Cam Ranh Bay base lies in of one of the region's best natural harbours and the United States sees it an ideal spot to bolster an American naval presence in the strategically vital South China Sea.
China claims all of the South China Sea, which is believed to encompass huge oil and gas reserves. One-third of global seaborne trade passes through the region.
Hanoi and Beijing have rival claims to the Spratly Islands and a long-standing dispute over the Paracel island group.
A more aggressive approach from China in the South China Sea has prompted Vietnam to forge closer defence cooperation with its former foe the United States, analysts say.
"Vietnam is arguably the crucial swing swing state when it comes to the South China Sea," according to a recent report from the Center for a New American Security, a US-think tank with close ties to President Barack Obama's administration.
"If Vietnam does not resist China's rising power, weaker and less assertive states such as the Philippines have little chance of blocking Chinese hegemony," said the report.
On a nine-day regional tour, Panetta's visit to Vietnam follows a speech on Saturday at a security summit in Singapore in which he said the US Navy would shift the majority of its ships to the Pacific by 2020, as part of a strategic focus on Asia.
