I think the solution to this problem is being able to select which end of the runway you want to start at, even at a one-runway base. This will also help you by being able to takeoff in the proper direction without having to make 180 turns while you're still low and slow. I never tried this, but you could try having someone take out a B17 and the fighter will start "inside" it, letting the B17 take all the damage while the fighter taxis out of it's "shell." The fighter can then become airborne while the B26 scrambles to get itself in the air

I recall saving a field by just being persistant. The B26 extinguishes it's nose ammo relatively quickly, so taking up B17 after B17 usually does the trick.
I do not think that disabling guns on the ground is the solution. You always want the option of being able to kill that sloppy vultcher who happens to cross your sights. A fighter could very easily do what the B26 is capable of, although it will have to get much closer to the enemy.
Here's a pic of me and a teammate keeping a field supressed....the lone time I ever used the B26 this way. I was practicing low level bombing without the sight before landing, hence the craters. Nobody ever bothered to defend this field so our services weren't neccessary

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Mark VanZwoll
33rd Strike Group