Cash for the "vital" Ministry of Defence programmes has been found as a result of austerity measures, the Prime Minister will say.
The funding pot includes an extra £800 million of investment in an intelligence, surveillance, target acquisition and reconnaissance package, which includes unmanned aircraft.
It will bolster special forces' ability to deal with the threat of global terrorism and hostage-taking, according to No 10.
Mr Cameron will say: "Having modern, technologically advanced and flexible armed forces to protect us and our interests is vital.
"Because of the decisions we have taken to tackle the deficit we are able to make investments in defence.
"We are also taking action to sustain our thriving defence industry, as part of our long-term economic plan to create jobs and secure a brighter future for hard-working people."