Defence Secretary Philip Hammond has said he is "very confident" the Army can reach its target of 30,000 reservists by 2018, despite concerns the recruitment drive has started slowly.
Under Government plans the regular Army is being cut from 102,000 to 82,000 while the newly-renamed Army Reserve - formerly the Territorial Army - is being expanded from 19,000 to 30,000.
Speaking at a recruitment event for all three armed forces on Horse Guards Parade in central London, Mr Hammond said reservists will be crucial to the future make-up of the military.
" They will be critical to mounting military operations in the future - an integral part of the armed forces," he said.
"We're very confident that we will achieve this target. It's a challenging one, but the army is used to challenges, and as this campaign ramps up - and today's event is an important step in that process - we're seeing more and more contacts.
"Over time they will convert into trainees in the pipeline to delivery as trained reservists in a couple of years time."
Mr Hammond drank tea with troops as he looked around various stalls set up on Horse Guards Parade.
Hundreds of visitors clambered around military trucks, posed for pictures with soldiers in camouflage and drove remote-controlled bomb disposal vehicles.
Last month, a leaked Ministry of Defence memo warned w ould-be part-time soldiers were being put off from signing up due to defence cuts and a "hostile recruiting environment".
It claimed there had been "disappointing" numbers of reservists being recruited, with fears that targets will not be reached.