I'm sorry, the worst attack you can make on a B-26 is what I did last night...
I upped in a G-10 with 75% fuel, external tank, gondolas and a 30mm with the express intent of buff hunting. After getting up to 15k or so I spotted a B-26 and after a couple minutes worked my way to co-alt and about 2k off his 9. My intent was to burn a little speed gaining a bit of altitude and then make a downward slash across him counting on the 30mm to work its magic. If I miss timed it I would simply continue the arc down to extend and then give it another try.
As I began the slash I noticed that a friendly I had spotted earlier was closing on the 26's 6. About that time the 26 started firing at the friendly. "Oh Ho!" thinks I, "He's not looking at me!" and turn the slash into a roll out just behind the 26. As the sight crosses wing of 26 I fire both cannons and mg and see about three hit sprites on the wing and then ... nothing. "What the frick," I think, "I got a 30mm?!?! How can this be?!?!"
About this time the 26 starts to ping me and I quickly roll way. A moment later the friendly takes the 26's wing off and gets a well earned kill. Safe I glance and the instruments and think dumbly for a moment, "Hmm, nothing is showing in the ammo counter for my cannon. That's weir.... OH NO!"
You guessed it, I had the ext tank displayed. I rolled in behind the bad guy, pinged him with a few 13mm's and then "dropped my tank at him."