April 25 (Reuters) - North Korea celebrated the 75th birthday of its army on Wednesday, calling it an "invincible revolutionary force".

Here are some facts about North Korea's military.

NUMBERS:

-- North Korea's 1.2 million-strong military is the world's fourth largest in terms of active troops after China, the United States and India. The North remains technically at war with the South, which has a 670,000-strong military, because the 1950-1953 Korean War ended with a truce and not a peace treaty.

-- Most of the North's army is deployed near the 248-km (154-mile) long Demilitarised Zone (DMZ) border dividing it from South Korea.

RATIO:

-- The communist state has the world's highest military/civilian ratio: 558 military personnel per 10,000 people; more than twice second-place Israel's 251 per 10,000.

-- Military service is compulsory for men; women also receive training.

EQUIPMENT:

-- North Korea has more than 800 ballistic missiles. It has more than 1,000 missiles of various ranges in total.

-- The backbone of North Korea's air force is an ageing fleet of 780 fighters and 80 bombers built with Soviet technology, the South's Defence Ministry said.

-- The North has about 3,700 tanks and 2,100 armoured vehicles, 420 battle ships and 60 submarines.

-- The North conducted its first nuclear test in October but proliferation experts do not think the secretive state has the technology yet to miniaturise an atomic warhead to mount on a missile.

Sources: Reuters, South Korea's Defence White Paper 2006; The Military Balance, 2007; The Top Ten of Everything, 2007; South Korea's Defence Ministry; Japan's Ministry of Defence (www.mod.go.jp/e/publications/defense1996/chapter1/section3/2_2. html) ((Writing by Gill Murdoch and Seoul Bureau, editing by Bill Tarrant; Singapore Editorial Reference Unit, gill.murdoch@reuters.com, Reuters Messaging gill.murdoch.reuters.com@reuters.net; +65 6870 3922)) REUTERS jh JK

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