You mention the a-10 but it is relevant today, and fyi tankbuster was not ever in it's intended design, it was designed from the ground up as cas not as a tankbuster, it just happened to fill that role nicely. The predecessor to the a-10 the a-1 was designed as a torpedo launcher and bomber to take out aircraft, it's own design too was obsolete as ww2 ended before it was ready, but due to it's high weight capacity was redesigned into a cas aircraft, the tech proved valid but it's original purpose not, so itwas turned into one of the most feared cas aircraft known.
OK, got ya. OK, now a little history lesson.
When the Air Force put out a call for a replacement Attack aircraft (something they do not even want to do, but they are mandated to provide one by the Key West Agreement), they created the A-X project. And there were 2 designs submitted. That is the Northrup YA-9, and the Fairchild YA-10. Both aircraft were remarkably similar, and if you set both of them at 100 meters and block off the view of the nose most would likely be unable to tell them apart.
But the difference between the 2 was the GAU-8 cannon. In fact, a weapon that is remarkably lousy in use for a CAS aircraft. The Army actually preferred the YA-9 with the smaller 20mm Vulcan cannon, as it had almost double the ammo capacity of the 30mm GAU-8. But the Air Force had the final say, so the YA-10 won and the YA-9 lost.
It assumed the role of "Tankbuster" because in the then battle plans for a NATO-Warsaw Pact conflict, it was realized that the main threat would be Soviet tanks and not infantry. And our own forces would be conducting a fighting withdrawal and not actually conducting the kind of defensive actions where CAS would be of any great use (beyond what the Army's own rotary wing aircraft could provide). You call in CAS when you really need to hold a location. Otherwise you simply slip away. That is what the entire battle plan for WWIII in Europe was. No big fights, little attacks then running away.
Remember, the A-10 is by it's designation an "Attack" aircraft. Not an F for Fighter, or B for Bomber. And attack means going after ground targets. If it was only intended for CAS, then they would have selected the YA-9, not the YA-10. The 9 was a much better CAS aircraft, but the 10 was much better at taking out other ground targets (like tanks,something the 9 really could not do well).
Under that order of battle, the A-10 was tasked with 3 main roles. Taking out tanks, taking out logistics trains, and taking out command and control centers. Notice, those are all "Attack" roles, as the designation of the aircraft mandates. But they re not really CAS roles. It would however slip back into it's CAS role when NATO went back on the offensive once the Warsaw logistics lines had been stretched to their limit, and the number of tanks thinned.
But no, it was not really a CAS aircraft. Notice how early on I stated that the Air Force was mandated to provide an
Attack aircraft. Not a CAS aircraft. CAS is a role in an Attack aircraft, but not their only role. Their actual role is to focus almost exclusively upon ground targets and not air targets But it was always intended in the role of taking out ground targets, more specifically tanks and not troops in the open. And in the traditional CAS role, it does not rely upon it's canon so much. Instead it primarily uses it's rocket launchers.
The only branch that really has it's own CAS aircraft is the Marines. The AV-8B is really the only fixed wing CAS aircraft the US really fields. It's air defense capabilities are very limited, and it's ground attack is also limited. But because it operates much like a rotary wing aircraft in many ways it is an excellent CAS platform.
But those are being retired in a few years, and replaced by another similar aircraft, the F-35B.
