The guided missile carrier USS McCain and the aircraft carrier USS George Washington are taking part in the non-combat training exercises in the South China Sea.
The exercises celebrate 15 years of diplomatic ties between the former enemies after aggressions ended in 1975 when the communists over ran the South Vietnamese capital Saigon, now called Ho Chi Minh City.
The two countries have been drawing closer through increased trade and cultural exchanges, especially since a visit in November 2000 by U.S. President Bill Clinton to Hanoi. It was the first presidential visit since the end of the Vietnam War.
The USS McCain "is hosting training and engagement opportunities between American and Vietnamese sailors as well as be a focal point for local community-outreach activities," a U.S. State Department statement said.
Sailors will take part in "medical and dental civic-action projects, an underway aircraft carrier embark, and ship visits," as well as a volleyball game and a barbecue.
At sea, exercises will include shipboard damage control, search-and-rescue demonstrations and "cultural-skills exchanges" such as cooking events.
In Da Nang, the former U.S. Navy base during the Vietnam War and where the McCain has been docked, U.S. naval personnel will conduct community-outreach projects at a school and an orphanage, the State Department said.
"This is indicative of the increasingly closer ties between the U.S. and Vietnam," U.S. Navy Rear Adm. Ron Horton, commander of Task Force 73 and Logistics Group Western Pacific, said.
"Exchanges like this are vital for our navies to gain a greater understanding of one another and build important relationships for the future."
The United States was Vietnam's top export market as well as its largest foreign investor in 2009. Trade between the two countries amounted to $15.4 billion, part of a rebuilding of confidence between the two countries, U.S. Secretary of State Hillary Clinton said on a visit to Vietnam last month.
Both countries have "made an intensive effort to rebuild ties that increase engagement on issues as diverse as health and human rights, energy, security, defense, and most certainly business, trade, and investment," she said.
U.S. investment has helped expand economic opportunity in Vietnam, even as Washington continues to push for greater political freedoms within the country, she said.
"This is not a relationship that is fixed upon our differences. We have learned to see each other not as former enemies, but as actual and potential partners, colleagues and friends. This tradition of cooperation is bringing great benefits to us both," Clinton said.
But China, Vietnam's neighbor, has voiced concerns over the exercises, as well as U.S.-Vietnam talks on the transfer of nuclear technology for energy needs to Vietnam, an important nuclear technology export market for China.
China also is concerned that Vietnam could use nuclear technology to enrich uranium for export.
Vietnam has bilateral nuclear co-operation agreements with China as well as Russia, France, India, South Korea and Argentina. It also signed in March a memorandum of understanding on nuclear energy cooperation with the United States.
This week, a Vietnam foreign ministry spokesman said negotiations are continuing with the United States about a civil nuclear cooperation agreement. It covers the issue of Vietnam not passing on nuclear materials, equipment and technology to other countries to ensure that nuclear weapons are not proliferated.
Vietnam is a signatory to the Nuclear Non-Proliferation Treaty but the country is speeding up the use of nuclear energy for peaceful purpose, the representative told reporters.
China is watching carefully the exercises. It claims large areas of the South China Sea as its territorial waters because it lays claim to the hotly disputed Spratly and Paracel islands.
But Vietnam, as well as Taiwan, Malaysia, Brunei and the Philippines, also claim all or some of the islands.
At stake isn't so much the tiny islands themselves, a collection of more than 700 reefs, atolls and cays whose total land mass is measured in several square miles, depending on tides.
Of greater importance is that ownership allows control of the surrounding militarily strategic shipping lanes and economically important fishing grounds and oil and natural gas reserves.
"The strategic implications and importance of the waters of the South China Sea and the freedom of navigation is vital to both Vietnam and the United States," Capt. Ross Myers, commander of the George Washington's air wing, said aboard the ship during a VIP visit of Vietnamese officials Sunday.
"I'm certain that the Chinese government and the Chinese people are trying to protect their interests. It is more important for Vietnam (and) its partners to establish that they have an equal right to economic prosperity and peace within the region as well."