During his flying visit he told troops: "We will do everything we can to support you with the equipment necessary and the resources you need."
On Friday Mr Brown also told the Iraq inquiry that, when he was chancellor during the 2003 war, no military requests were refused.
He said: "At any point, commanders were able to ask for equipment that they needed and I know of no occasion when they were turned down."
But Lord Guthrie, ex-chief of the defence staff, told the Daily Telegraph armed forces had been denied a request for more helicopters.
He said: "He cannot get away with saying 'I gave them everything they asked for'. That is simply disingenuous."
And his successor, Lord Boyce, told the Times: "There may have been a 1.5% increase in the defence budget but the MoD was starved of funds."
Caroline Wyatt, BBC defence correspondent
The Army asked several years ago for a range of thousands of armoured vehicles in a procurement project known as the future rapid effects system - a project beset by delays and changes of plan.
What has happened instead is that the Army has relied on a series of different vehicles from various manufacturers to deal with the rising threat from roadside bombs.
Much has been spent as a result, and many of those vehicles have proved their worth. But when the Snatch Land Rover was banned from use outside UK military bases in Helmand, commanders were left with few smaller, more manoeuvrable vehicles to use in more benign areas.
Heavier, better-protected vehicles are popular but not always practical. So a new lightly-protected patrol vehicle will be useful, though it's unlikely to be taken into areas where the threat from roadside bombs is highest.
And no armoured vehicle offers absolute protection. The military will have to continue with efforts to dismantle the networks behind the bomb-makers, and try to ensure that there are enough bomb disposal experts to dismantle the devices when they have been laid.
Shadow defence secretary Liam Fox said the defence secretary had already announced on 15 December that the new armoured vehicles would be introduced.
He told the BBC: "We get the news re-announced the day after the prime minister gives evidence at Chilcot, when former defence chiefs say he wasn't telling the truth about armed forces funding.
"This is not the way to treat our armed forces and I think there will be a lot of people in the armed forces very unhappy at being used as political props today."
However, the MoD told the BBC the announcement referred to completely new vehicles.
Other opposition parties joined in the criticism with Liberal Democrat defence spokesman Nick Harvey saying while it may be "literally" true every formal request for equipment for Iraq was met, the requests were always made under a financial constraint.
The Scottish National Party's Westminster leader Angus Robertson said the PM "must appear again" before the Chilcot inquiry following the military chiefs' criticisms.
In a swift tour which took in bases captured only weeks ago from the Taliban, Mr Brown met and thanked some of the 4,000 British forces who took part in the opening phase of Operation Moshtarak.
The PM said: "I am here because I want to thank the British troops for their bravery, their dedication and their professionalism."
He added it was "important to come at this stage to see what progress has been made on this first operation under a new phase of action in Afghanistan".
Shadow defence secretary Liam Fox accuses PM of using armed forces as "political props"
His aides said that Defence Secretary Bob Ainsworth will announce within weeks the £100m investment in the new British-built vehicles, which should arrive in Afghanistan by late 2011.
The new patrol vehicles are smaller and lighter than the Mastiff and Ridgeback armoured personnel carriers which are already taking over some of the tasks of the more vulnerable Snatch.
They also said an additional £18m will also be spent on equipment and training for Afghan forces to deal with the improvised explosive devices (IEDs) used by the Taliban.
And 150 new instructors from the UK police and Army will also be deployed to train Afghan police.
Mr Brown's visit came on the same day the deaths of two soldiers from 3rd Battalion The Rifles were announced.
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