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Ulchi Freedom Guardian is one of the largest military exercises in the world.

The war games, which last year ran for 11 days, have involved some 17,500 U.S. forces, including about 3,000 from outside the peninsula, and 50,000 South Korean troops.

The exercises include computer simulations carried out in a large bunker south of Seoul intended to check the allies’ readiness to repel aggressions by North Korea.