The short answer? The sky. Following World War II, US junkyards and surplus stores were filled with an abundance of leftover warplane parts, which included plenty of drop tanks, or belly tanks.

After World War II, with much of Europe and East Asia in ruins, American factories shifted from tanks and rifles to cars and washing machines. The U.S. postwar trade surplus peaked at $12 billion ...

HANOI, Feb 5 (Reuters) - Vietnam's trade surplus with the U.S. soared to a ... both major beneficiaries of the last U.S.-China trade war, as manufacturers based in China moved production overseas ...