What was the world's first practical all metal aircraft?

The Junkers J 1, nicknamed the Blechesel ("Tin Donkey" or "Sheet Metal Donkey"), was the world's first practical all metal aircraft. Built early in World War I, when aircraft designers relied largely on fabric covered wooden structures, braced with struts and exposed rigging lines, the Junkers J 1 was a revolutionary development in aircraft design.

Specifically, the Junkers J 1 was a mid-wing monoplane with a cantilever wing, without exterior bracing struts or wires. External bracing was only used for support of the horizontal stabilizer and the undercarriage.

Although considered heavy, cumbersome, and slow to take off from rough airfields, the Junkers J 1 was immensely strong and well suited for low level fighting and aerial observation. As a result of its weight, the J 1 was known to be a truly slow aircraft. Nonetheless, it provided effective protection against ground fire in World War I.