Next year will mark the 40th anniversary of the fall of Saigon and the end of the Vietnam War. Over 50,000 US servicemen died in the decades-long conflict and thousands of Vietnamese soldiers and civilians also perished. The war finally came to an end in 1975 when the US ignominiously withdrew and North Vietnam forces overran the south to reunify the country under communist rule.
The conflict left deep scars for both countries. From 1975 onwards, the US Government established a trade embargo against the newly formed communist state and diplomatic relations were cut off. Both sides regularly clashed on issues relating to the war including US servicemen still missing in action and, for Vietnam, unexploded ordnance and the US military's use of hazardous chemicals such as Agent Orange.
But in the last two decades, US-Vietnamese relations have improved and the former foes have become increasingly close. In 1995, then- president Bill Clinton announced the formal normalisation of diplomatic relations between the US and Vietnam, closely followed by the opening of a new US Embassy in Hanoi. Military relations were established a year later.
In 2000, Bill Clinton became the first US president to visit Vietnam since the fall of Saigon. Top-level US and Vietnamese officials now regularly meet in Hanoi and Washington to discuss economic, political and defence issues. Vietnam is now one of the US's biggest trading partners in the region and key economic partner.
Vietnamese president Truong Tan Sang met President Obama in the Oval Office last year. Both countries launched the Comprehensive Partnership during Sang's visit, which laid the groundwork for greater cooperation in trade, technology, education and, importantly, defence.
"I think it signifies the maturing and the next stage of the development between the United States and Vietnam," President Obama said during Sang's visit. "As we increase consultation, increase cooperation, increase trade, and scientific and education exchanges, ultimately, that's going to be good for the prosperity and opportunities of the people here in the United States, as well as good for the opportunities and prosperity of the people of Vietnam."
The US 'rebalance' to Asia and strategic relations
Closer ties to Vietnam have also taken on a greater, more strategic, significance since the US announced its 'rebalance' strategy to Asia. A recent report by the Centre for Strategic and International Studies said both Washington and Hanoi's strategic interests in the South China Sea align, especially in light of China's recent aggression in territorial disputes.
"Both believe that freedom of navigation and commerce should be preserved and call for a peaceful, rules-based approach to address long- standing territorial disputes; yet both want to avoid using military aggressiveness or other forms of escalation if possible," the report, co-authored by Phuong Nguyen, said.
Governments often recruit private military and security companies to bolster regular troops and support services.
In 2010, the US and Vietnam initiated the annual Defense Policy Dialogue (DPD) between the two countries' respective defence departments. During the fourth DPD in 2013, the US and Vietnam Coast Guard signed a cooperation agreement on training and curriculum development. Shortly afterwards, secretary of state John Kerry announced $18m in assistance to enhance Vietnam's maritime capabilities.
"Peace and stability in the South China Sea is a top priority for us and for countries in the region," said Kerry during a trip to Hanoi late in 2013. "We are very concerned by and strongly opposed to coercive and aggressive tactics to advance territorial claims."
Vietnam's concerns about an increasingly assertive China were strengthened earlier this year when a massive oil rig - owned by the China National Offshore Oil Company Group - was deployed to a disputed area near the Paracel islands in the South China Sea. Vietnam said the rig was inside its exclusive economic zone, which China disputed.
China's brazen move triggered weeks of anti-Chinese riots in Vietnam. The rig was eventually moved but relations are now at their lowest point since the two communist countries fought a brief war in 1979.
US officials have seen this as a good opportunity to relax the country's strict lethal arms embargo against Vietnam, which has been in place for nearly 40 years, and begin the process of building maritime capacity in the region. On 2 October US State Department spokesperson Jen Psaki announced the US would be taking steps to allow the future transfer of "maritime security-related defense articles" to Vietnam to bolster maritime capabilities.
Moving beyond diplomatic rhetoric - Vietnam to buy the P-3?
Two conclusions can be drawn from the US's partial lifting of its embargo, says Carl Thayer, a Southeast Asia specialist and Emeritus Professor at the University of New South Wales. "First, the United States policy to counter Chinese assertiveness in the South China Sea has moved beyond diplomatic rhetoric...Second, the change in US policy also has the effect of undercutting party conservatives in Vietnam."
US officials are, however, keen to stress that it does not mean they will provide Vietnam with any kind of lethal assistance. The floodgates aren't opening, one official was reported as saying.
Instead, the US Government will likely approve defence sales on a case-by-case basis. "The most logical system for them to buy would be used P-3 Orion [maritime patrol aircraft] from the US Navy and Lockheed," says Richard Aboulafia, vice president of analysis at Teal Group. "We're not going to sell them the P-8 [Poseidon], which is the US Navy's replacement from Boeing - that's not going to happen."
Vietnam would join a growing list of countries in the region which are operating the P-3 Orion. That list includes Taiwan, which received its first P-3 in September 2013, Australia, New Zealand, Japan, South Korea and Thailand.
Another platform which could suit Vietnam's needs and be used "in a wide variety of roles" is the C-130 transport aircraft, explains Aboulafia. The C-130 Hercules could be used for cargo transport, maritime search and rescue, resupply by air and maritime surveillance. "There's a large number of used C-130s available," says Aboulafia.
Vietnam still relies heavily on Russian defence equipment, which is expected to continue despite the lifting of the US arms ban. Some estimates suggest Russian equipment made up 95.8% of Vietnam's defence imports during 2009 and 2013. The navy, for example, is procuring a new fleet of Russian-made Kilo class submarines and its air force is receiving a batch of new Sukhoi SU-30 fighter jets.
A benefit of buying Russian equipment is that you pay less up-front compared with western kit, explains Aboulafia, but in the long run you pay more in terms of maintenance and support. That's something Vietnamese officials will have to learn for themselves as they begin to buy and integrate more western defence equipment, such as the Airbus C212-400 maritime patrol aircraft currently being operated by the coast guard.
India and Japan - which, like the US, are concerned about China's growing military capabilities - have also entered into agreements with the Hanoi government to supply defence equipment. India agreed in October to supply four naval patrol vessels to Vietnam as well as expand training programmes and joint exercises. A similar arrangement for six naval ships was agreed between Hanoi and Tokyo in August.
Russia’s annexation of Crimea and the withdrawal of NATO forces from Afghanistan has seen military planners reassess their approach to future land warfare.
US strategic interests vs. human rights
The US has made the lifting of arms restrictions dependent on Vietnam's commitment to improving human rights for its citizens. According to Freedom House's 2014 'Freedom in the World' report, Vietnam was among the countries with the worst scores for political rights and civil liberties. John Sifton, Asia advocacy director for Human Rights Watch, says Vietnam is a "non-democratic, one-party state with an abysmal human rights record".
"Unfortunately, the decision to relax the lethal arms ban has already been made," said Sifton. "It is not too late, however, to use remaining leverage to achieve change. Given the absence of real reform to date, and the major steps that remain to be taken, the US should communicate to Hanoi that it expects much more before the ban will be lifted further."
The question is what the US values more; a strategic partner in Southeast Asia that can counter the growing threat from China, or advancing international human rights? Unfortunately for activists in Vietnam, the US has shown that strategic interests can often trump human rights concerns; Egypt and Saudi Arabia are key examples in the Middle East.
Human rights could certainly complicate US-Vietnam bilateral relations and will have to be approached with care in future meetings. Defense Secretary Chuck Hagel, himself a Vietnam War veteran, is expected to visit Vietnam soon. That could open up more defence opportunities and strengthen existing military ties under the DPD and Comprehensive Partnership.
While challenges remain, it's still extraordinary to imagine that only forty years ago the two sides were sworn enemies.