BBC's Newsnight program spoke to Korean defector Joo-il Kim, who says he was an anti-tank battalion commander in North Korea's army for seven years until he fled the country in 2005.
According to Mr Kim, Pyongyang's lack of access to enough new conventional weaponry is what drives its controversial nuclear programme.
"Conventional weapon-wise, North Korea is better equipped than South Korea. But most of the weapons are outdated and so, to make up for that weakness, the North concentrates on missiles and nuclear arms development."
North Korea is believed to have more than 800 ballistic missiles, including long-range missiles.
"Officially the North Korea armed forces number 1.2 million - these are the official numbers," Mr Kim said. "About 100,000 people are conscripted annually and they serve for 10 years," he added.