I think it might be a cover to increase range when they're doing long range flights, when no combat is anticipated
Covering that big blunt cannon muzzle with something somewhat streamlined would have to help drag wise.
I recall the day they phased out the KC-97, when I was at Tinker AFB. They found a bad corrosion problem on one airframe where the MLG attached to the wings. They inspected the others and found they all had it. That was that; the directive came out to fly them all to the boneyard. One advantage the KC-97 had over the KC-135A was that the reversible props enabled them to handle icy runways better.
One AF Reserve unit located on Tinker had been equipped with KC-97. They transitioned to F-105D (!!!)
I saw an early test film of an A-10 firing its gun. At that time the gun muzzle was almost recessed into the nose. The excess gun gases came out and ignited right in front of the nose, producing about a 6 ft diameter fireball that did not enhance accuracy. So the added a suppressant to the gunpowder to stop that. The next thing was that the A-10 SPO people came to talk to the A-7D people about how they handled the corrosion from the M-61. The A-7D had no corrosion problem from teh gun but the suppressant they added to the A-10 powder was corroding the hell out of the airframe. Next change was the gun stuck a lot further out of the nose, which I assume was an alternative to the suppressant.
F4U-4 Corsair fighters of U.S. Marine Corps attack squadron VMA-332 Polka-dots aboard the escort carrier USS Point Cruz (CVE-119) on 27 July 1953 during a deployment to Korea
Source warship wednesday – laststandonzombieisland