The A-10 is justifiably celebrated for its tank-killing prowess.
After all, it destroyed 987 tanks and a metric buttload of other Iraqi stuff during Desert Storm, and its GAU-8 got a lot of use, including some Iraqi helicopters who felt the BRRRRT! But the Air Force once planned for a tank-buster with a gun that made the A-10's GAU-8 look puny.
The Beechcraft XA-38 Grizzly was intended to be a close-air support plane to bust up tanks and bunkers in front of the infantry. Beechcraft, ironically, is best known for civilian planes like the King Air.
Beechcraft XA-38 (S/N 43-14407) in flight. (U.S. Air Force photo)
To accomplish that mission, it was given a powerful armament. In the nose was a pair of M2 .50-caliber machine guns and a powerful T15E1 75mm automatic cannon. It had a pair of twin .50-caliber turrets as well (one on the top, one on the bottom), and the ability to carry up to 2,000 pounds of bombs, according to MilitaryFactory.com.
Yeah, you read that right. The Army Air Force in World War II was developing a specialized tank-buster that was two and a half times bigger than the GAU-8. Of course, a 75mm gun had been used on variants of the B-25, but the XA-38's gun was essentially a semi-auto.
A parked XA-38, with the barrel of the T15E1 prominently visible. Makes the GAU-8 looks like a cute popgun doesn't it? (U.S. Air Force photo)
The plane had a top speed of 376 miles per hour, a range of 1,625 miles, and a crew of two. With all that performance, it had a lot of promise when it first flew in May of 1944. But that promise was never seen by the grunts on the ground.
The XA-38 project never got past the two prototypes, because a different aviation project took up all the engines that the Grizzly was designed to use. The Wright GR-3350-43 engines were needed by the Boeing B-29 Superfortress, which in 1944 was needed to bomb Japan.
One prototype was scrapped, while the other's fate remains unknown.