The U.S. and South Korean militaries will stage a large-scale exercise off the west coast of the peninsula from this weekend, just days after North Korea fired a barrage of missiles at a South Korean island. The nuclear-powered USS George Washington will participate in the exercise from Sunday to the following Wednesday. Here are some questions and answers about the exercise: WHY CONDUCT JOINT EXERCISES? The exercises are held primarily to send a message to North Korea that the U.S. military stands by South Korea. These combined drills are also an overt show of force. Washington says large-scale drills, which started after the sinking of the Cheonan warship in March, are designed to send a clear message to North Korea that its aggressive behavior must stop. The U.S. and South Korean militaries are vastly better equipped than the North's, and experts say they would quickly win any war. The North's force of over a million troops easily outnumbers the U.S.-South Korean contingent, but its equipment is old and it barely has enough fuel to fly its fighter jets. The exercises also serve to underline the gap in technology. HOW OFTEN AND WHERE ARE THEY HELD? South Korea and the United States hold combined exercises each year, but after the sinking of the Cheonan they agreed to stage a series of large-scale military drills. This weekend's exercise will be their third of these extra combined maneuvers, and the second to take place near where the Cheonan was torpedoed in the Yellow Sea. North Korea denies responsibility for the attack. A joint drill in July involving the aircraft carrier the USS George Washington was initially planned for the Yellow Sea off the peninsula's west coast, but after criticism from China it was moved to areas off the east coast. This weekend's drill had initially been scheduled for late last month, just before the G20 summit in Seoul, but was postponed due to scheduling problems. WHAT IS THE SIGNIFICANCE OF SENDING AN AIRCRAFT CARRIER? The participation of 97,000-ton nuclear-powered carrier from the U.S. 7th Fleet is the ultimate show of strength. Carriers have a become a symbol the United States' position as a superpower. The carrier strike group includes 75 aircraft and 6,000 sailors. These massive vessels, essentially mini cities at sea, have found an important role as the "forward military presence" of the United States. The United States has 11 carriers in service around the world, about twice as many as the rest of the world. WHY DOES THIS UPSET NORTH KOREA SO MUCH? Pyongyang regards military exercises by South Korea and the United States with genuine unease, fearing the maneuvers could be a smokescreen for a real attack. The North customarily responds to such exercises with bellicose remarks. In July, it threatened "a sacred war" if the allies went ahead with joint exercises. On Thursday, it said it "will wage second and even third rounds of attacks without any hesitation if warmongers in South Korea make reckless military provocations again." The North says the exercises also violate its sovereignty and pose a major danger for the security of the region. WHY HAS CHINA REACTED SO ANGRILY TO THE EXERCISES THIS YEAR? China has in the past given two reasons for its opposition to the drills. Firstly, it says they add to tensions in the region, which have been running high since the sinking of the Cheonan. Tuesday's shelling of a remote island village raised tension levels another notch. Secondly, China says the exercises threaten its own security, happening too close to home shores for comfort. Beijing has also been irked by U.S. Navy ships engaging in surveillance in waters close to its coast. The United States says the Chinese should have no concerns with these types of exercises because they take place in international waters. More broadly, China fears being encircled by hostile forces, whether Russia to the north, India to the southwest or U.S. military bases in Japan and South Korea. (Editing by Nick Macfie and Ron Popeski) (jeremy.laurence@reuters.com; Reuters Messaging: jeremy.laurence.reuters.com@reuters.net; +822 3704 5510)