The U.S. and South Korean militaries conducted a joint river-crossing drill Wednesday, the latest exercise in a large-scale operation designed to counter North Korea's own escalating military drills.

Main battle tanks and other armored vehicles crossed the temporary bridge over the Namhan River south of the capital of Seoul. U.S. and South Korean engineering teams constructed the bridges in a matter of hours using pontoons dropped from trucks, Reuters reported.

Boats pushed the pontoons into position to assemble the crossings, which would allow for troop and vehicle movement in the event of a key bridge being destroyed. The temporary crossings could also allow U.S. and South Korean forces to avoid using major infrastructure landmarks entirely.

While the border between North and South Korea is made up of multiple rivers, military officials told Reuters that Wednesday's operation was purely defensive.

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The drill involved 1,000 South Korean and U.S. troops, as well as 50 vehicles, including tanks, KF-16 fighter jets and Apache and Cobra attack helicopters. The helicopters could be seen passing over the completed bridge and firing flares. The bridges themselves consisted of more than 140 pieces of engineering equipment, according to Reuters.

The exercise comes days after Kim Jong Un's regime in the North fired a missile and artillery shells into the sea, marking the North's 15th ballistic missile launch since late September.

North Korea has grown increasingly aggressive since the U.S. and South Korea began joint military exercises in September. The operation coincided with a visit to Seoul by Vice President Kamala Harris.

North Korea also flew 12 warplanes near the South Korean border earlier in October. The sortie included eight fighter jets and four bombers. South Korea responded with a flight of 30 warplanes, but the two groups did not engage.

The allied drills have not been without mishaps, however, as a South Korean ballistic missile South Korean ballistic missile malfunctioned and exploded on the ground in early October.

U.S. military officials clarified that the warhead on South Korea's missile did not explode, but the propellant caused a large blast and flames. The incident caused many local residents to fear that an attack from the North was underway, and the military didn't clarify the cause of the explosion and flames for hours.