During a trip to Afghanistan on Armed Forces Day, David Cameron said it was an opportunity to say "how proud we are of our armed forces and everything they do for us".
He also said funding from Libor rate-rigging fines would be put into military charities and a permanent memorial would be built at the National Memorial Arboretum in Staffordshire.
In terms of the political aims of the country, he said: "We want a political solution as well as making sure we have a security solution.
Mr Cameron added that it was important that the politics "enable everyone in Afghanistan to play a role in the future of their country".
More top news
Charities warn that sitting down too long can lead to health risks such as type 2 diabetes and cardiovascular disease.
The Labour leader will use a speech to set out the differences between his party and the Conservatives with particular emphasis on the NHS.
Kate will join Prince William on a tour of the Stephen Lawrence Centre before visiting a charity working with disadvantaged young people.