10 Francs Bell X-1

The Bell X-1 became the first aircraft to exceed the speed of sound in level flight on October 14, 1947, with Chuck Yeager at the controls — a fact the U.S. military kept classified for nearly a year after the event. The Democratic Republic of the Congo, reconstituted under that name following Laurent-Désiré Kabila's overthrow of Mobutu in 1997, built a modest foreign-currency revenue stream through commemorative silver issues marketed entirely to overseas collectors. This coin never circulated domestically.