SEOUL, South Korea — South Korea showcased a ballistic missile capable of carrying an eight-ton warhead and featured a flypast of a U.S. bomber at military parades in Seoul on Tuesday, a show of force now held annually to signal readiness to respond to North Korean threats.

The Hyunmoo-5 missile, successfully tested last year, was displayed at the Armed Forces Day parade at a Seoul air base, involving some 5,300 troops, 340 types of military equipment and aircraft flypasts.

For decades such…