That war, which began in the early 1960s and ended with the fall of South Vietnam in 1975, saw ever larger numbers of US forces deployed and doomed the presidency of Lyndon Johnson.

The conflict was the deadliest for US forces since the Second World War, killing more than 58,000 US troops, at least 60 times more than have so far died in Afghanistan.

Legacy

The US humiliation in Vietnam continues to carry a bitter political legacy [AP]
At its height in 1968 the US had some 549,000 troops deployed in Vietnam, about eight times more than are currently in Afghanistan.

But despite those differences, the American humiliation in Vietnam carries a bitter political legacy and has frequently been used by critics of US involvement in Afghanistan who say the war is unwinnable.

Critics of the Afghan war have pointed to what they say are other similarities.

As with Vietnam the US is undoubtedly the superior military force and wins every fight it gets into, but ultimately makes little progress in winning the war.

In addition, critics argue that like Vietnam the US presence in Afghanistan is propping up a corrupt and ineffectual government that lacks popular support.

Presidential elections in Afghanistan earlier this year, which eventually saw Hamid Karzai returned to power, were beset by widespread fraud and allegation.

But in his West Point speech on Tuesday Obama hit back at those calling for the US to cut its losses and pull out of Afghanistan.

Unlike in Vietnam, he said, the US has been joined by a coalition of 43 nations in Afghanistan and was not facing a broad-based popular insurgency.

But he said the most important difference with Vietnam was that "the American people were viciously attacked from Afghanistan" adding that they remain "a target for those same extremists who are plotting along its border".