YB-40...http://www.kotfsc.com/aircraft/b17-v.htm
The initial Fortress "gunship", the XB-40, was modified from a Boeing-built B-17F by Lockheed-Vega and first flew in September 1942. The XB-40 bristled with 12.7 mm (0.50 in) machine guns. The Sperry ball turret and the Bendix ball turret were retained from the B-17F. The waist gun positions were increased to two guns each with power boost and were "staggered" to give the gunners more room. The twin-gun tail position was given power boost as well.
A second Bendix turret was added over the radioman's position, and a new Bendix "chin" turret was fitted under the nose, with the bombardier controlling it from a sight at the top of the nose Plexiglas. Armor was added for engine and crew protection. The XB-40 could carry about 11,000 rounds of ammunition, about three times that of a regular B-17F.
Flight tests at Wright Field suggested the idea had promise, and so 23 YB-40s were ordered, though only 19 were actually delivered. They were modified from Vega-produced B-17Fs by the Douglas plant in Tulsa, with the first rolled out in February 1943.
YB-40s arrived in England in April 1943 for combat evaluation. The results did not meet expectations. There were bugs and shoddy workmanship, but most importantly the YB-40 was simply too heavy. It could follow bomber formations well enough until they dropped their bombs, but then the bombers could take advantage of increased speed and altitude bought by the reduced weight.
The YB-40 was still loaded down with guns and ammunition and couldn't keep up with the formations on the way home. The program was cancelled in July 1943. Some YB-40s were sent back home and used for gunnery training as TB-40s. Although they were a failure, operational commanders indicated that the Bendix chin turret and the staggered waist gun positions were good ideas that should be incorporated into standard production.
Now, my point is, why havent we made an aircraft like a 707 or 747 or 757 or DC-10, that is a bristling array of Sidewinders or Sparrow or Phoenix missiles?
One of these, working with an AWACS or something like this RC-135, can shoot down anything flying at almost any range, and we can even carry custom missiles that have 3 hundred mile ranges, like a cruise missile, only radar guided.
Then, instead of an explosive warhead, we use a pulse weapon, like a massive EMP, that will fry the electronics of anything in front of it. That would take care of near misses, we only have to get within a mile to make a 'kill'.