Guess the weapon

After Pearl Harbor, the United States went to work on a top secret weapon to use on Japan. Here are some hints. Can you guess the weapon?

*This weapons program had the personal go ahead from Franklin D. Roosevelt.
*Scientists had to go out of their way to find the raw material for this weapon.
*Special casings and ignitors had to be designed for this weapon.
*The weapon was tested in the desert southwest.
*The weapon, if deployed correctly, would destroy thousands of buildings in Japan.
*The weapon was never deployed

Do you know what the weapon was?

It was the bat fire bomb.