Mr Cameron's visit saw him touring Camp Bastion in Helmand, where he viewed vehicles now surplus to requirements and which are being sent home after troop numbers were cut by 500 to 9000 this Christmas.
As well as being briefed by senior officers, he travelled to the smaller Camp Price base, 20 miles from Bastion, where he joined in a carol service with troops from 40 Commando Royal Marines.
He also took on one Marine at table football. After losing 2-1, Mr Cameron – who has faced speculation about his future as Tory leader – commented ruefully: "Someone better had better take over the blue team."
He had other defensive work to do when he backed newly announced plans for the British force in Afghanistan to be almost halved to 5200 next year.
Combat operations are due to end completely by 2014, but critics have warned that Western forces are cutting and running from their 11-year engagement in Afghanistan, potentially opening the door to a "Taliban resurgence".
But Mr Cameron believes Afghan security forces are getting the "capability" to control the country.
He said: "They are doing better than expected."
He admitted Afghanistan is still a "deeply challenged country", but insisted: "It is a far better place than it was when we came here in 2001."
The Government has pledged an extra £230million on military kit.