After the Germans called off their invasion of England it was clear to the Allies that, if they were to prevent the Germans to give it another try in the future, they had to attack them on their own territory. A prefered target was the Ruhr-area, as much of the German industries were building machines to support the war effort.
The only way to reach this target and to be sure of significant damage to the site, was to send in heavy bombers.

As the Americans joined the war effort in the European theatre, the B-17 "Flying Fortress" formations were a familiar sight in the skies of occupied Europe.
The bombers flew unprotected deep into occupied territory and over a well protected "Third Reich" in an effort to devastate the German production ability and thus slow down the entire war machine.
But the Luftwaffe had air superiority and wasn't going to let the bombers hit their targets without paying a price for it.
The Allied staff knew that the bombers would have a hard time getting to their target zones and back without any escort, but even if they wanted to send in fighters with them, there was just no fighter aircraft that had the range to follow their heavy friends all the way in and back. So for now they would have to depend on themselves for protection and repel the fierce Luftwaffe attacks with their own means.

The bombers were equipped with heavy machinegun stations placed in such a way that the whole area around the bomber could be covered.
The formations they flew made sure that the bomber crews were able to cover each other as much as possible. That way multiple bombers could target the same incoming attack to give the attacker a hard time placing a hit on the bombers.
A close formation of B-17's was a deadly opponent, and it was nearly impossible to attack a bomber formation from the classic "six o'clock" position.

Unless the German pilots had a death wish, there was just no way to attack the formations from behind without sustaining substantial damage or in much cases, destruction of the attacking aircraft. One of the "less defended areas" the earlier versions of the B-17's had was the front as they didn't carry much firepower in the nose of the aircraft.
So the FW-190 ,ME-109 (later on the ME-262,and others) pilots tried different approaches and found out that a frontal attack on these bomber formations minimized the time they were vulnerable to the B-17's defensive fire. During these attacks the Germans targeted the cockpits and engines of the bombers.
It took quite some skill as the closure rate during these head-on engagements were tremendous, leaving little time to aim and fire the MG's and cannons before they had to break off the attack and manoeuvre themselves to avoid a collision.
To counter this the allies removed the nosegun and added "chin-" and "cheekguns", giving the front of the bomber more punch.

As the head-on approach was a basic attack, other Luftwaffe pilots came in from the side's targeting the last bomber on one side as it was harder for other bombers to protect outside planes without hitting their colleagues.
In this type of attack the Germans aimed for the fuel tank area of the wings. Hoping to cripple them enough, forcing them to leave the relative safety of the formation, so they could destroy them without having to worry about the defensive fire of other bombers.

The only "six o'clock" attack was initiated at a range just beyond the defensive fire from the bombers. The Axis fighters launched timed rockets into the Allied formations.
Hoping to cripple them and leave the formation or in some cases destroy them with a direct hit.

The bomber raids intensified, and in an effort to bring the Luftwaffe to its knees they started hitting oil production and storage facilities, ball bearing factories, aircraft factories and so on.
But the plan backfired as the Luftwaffe's response was overwhelming having a peek on October 14 1943.
That day 229 bombers were on their way to bomb the ball bearing factory of Schweinfurt. The Germans destroyed 60 bombers and crippled 17 bombers that made it back but were beyond repair. A battle loss rate of 26.5%. The Germans losing 38 planes that day from all causes.

Luckily even before this horrifying event, the Allied strategists realized that the bombers needed long range fighter protection.
This is where the P-51B came into the picture, a fighter with the range to perform this duty.
The mission was to distract or if possible destroy any attacking aircraft that came near the bombers.
Escorting the bombers in flights of at least 4 Mustangs, they flew patterns around and above the bombers. The German pilots were ordered to ignore the escorts and attack the bombers as they were the primary targets.
This still resulted in severe casualties on the bombers side, but as the P-51 joined the battle from their superior altitude they were able to prove their value by destroying several attackers, sometimes even without losses on the escorts' side.

The P-51's turning rate was much better then that of the Me-109 and slightly better then the FW-190 , but where the FW's turning rate got worse in slow fights the P-51's was better then the FW's. The Mustang was also heavier than it's German counterparts and was able to out-dive them as well.
Later on the P-51D was equipped with a better engine (Rolls Royce Merlin engine), this gave the aircraft 300 extra hp than it's earlier version and included a supercharger that made it loose less speed at higher altitudes.

Later on as the number of P-51's increased in the European theatre they were ordered to sweep the area, covering a large area around the bombers, destroying any targets of opportunity. If possible these targets should be Luftwaffe assets, destroying German aircraft on the ground, taking off or on their way to the bombers. This made it very hard to reach the bombers and leaving them less time to attack thee bombers as they were aware that they could become targets themselves in a matter of seconds.

This was a big turnaround in the air war as the increased numbers of Allied aircraft also gave air superioruty to the allies.

As the war continued the Germans had to leave the air superiority role to the Allied aircraft, scattering their fighters around the country to make them less vulnerable to the Allied attacks.

I know this paper is far from complete, but I double-checked most of the information and I'm sure that the historic features are correct. If any of the readers can give me more information that could improve this document, feel free to contact me as I want to make this as perfect as possible. And your input is more than welcome.

As I would like to thank many people for research on the subject there are some special thx for Redwulf_1 , E.C. "BUD" Anderson and his son Jim as well as a lot of my team members who aided me in correcting and designing the original version.

Contact: Pacman@virtualtigers.com