General Doolittle's freeing of the fighters changed the attitude of American fighter pilots. Although some would say that Doolittle's decision merely gave free rein to the already existing attitude of American fighter pilots, the new philosophy required a tactical framework that allowed some freedom of operation for the fighter pilot while providing reasonable protection for the bombers. The new system quickly coalesced around four points:
1. Freeing US fighters from the restrictions of close escort.
2. Arrival in-theater of large numbers of US long-range fighter aircraft.
3. Development of the relay system of fighter escort.
4. Increased strafing of German ground targets by US fighter aircraft.
Coincident with the arrival of Spaatz and Doolittle, large numbers of long-range P-38 and P-51 fighter aircraft appeared in the theater while the range of the P-47 (already present in large numbers) was increased by 100 miles. This increase in numbers and range enabled the Americans to refine their escort technique. Large numbers of aircraft and an average of almost two pilots per plane permitted constant use of fighters. On any given day Doolittle could put several hundred fighters into the air.
Such numbers helped spur development of the relay system and buffered the casualties absorbed in ground strafing. Spaatz also had administrative control of all AAF forces in the United Kingdom, which allowed him to change P-51 allocations from the Ninth to the Eighth (giving the Ninth P-47s, an excellent ground-attack aircraft, in its place) and to ensure that Ninth Air Force fighter groups flew escort for the Eighth. The influence of numbers should not be underrated; they enabled all else. Spaatz's authority included the power of promotion, a weighty club to hold over the heads of recalcitrant Ninth Air Force personnel.
The differing escort ranges of the Eighth's fighter aircraft greatly influenced the system eventually adopted. The escort ranges of the fighters in comparison with the manufacturer's specifications represented only a fraction of the aircraft's rated capabilities. Several factors-the necessity to provide for an emergency combat reserve for each plane; the fuel consumed by delays in takeoffs, landings, and forming up; and less than optimum weather conditions-combined to limit a plane's range to, at best, three-eighths of its rated maximum. Escort imposed further range restrictions because of the speed difference between the bombers and their little friends. On penetration the bombers, usually carrying their full wartime emergency weight overload, averaged an indicated airspeed of 150 mph. The fighters, throttled back for optimum gas consumption, averaged at least 100 mph (indicated airspeed) faster. For example, P-47s that were not flying escort duty conducted sweeps well beyond Berlin-far beyond their escort range. To maintain stations with the bombers, the fighters had to zigzag, which subtracted from their straight-line range.
To maximize the amount of escort available to medium- and long-range missions, the Eighth Air Force developed a relay escort system. In this system instead of a single fighter group escorting a single bomber formation all the way to and from the target-an impossibility given a fighter group's range-a fighter group would fly straight to a prearranged rendezvous point with the bombers and escort them 150 to 200 miles to yet another rendezvous point where a second fighter group would pick them up, while the first group flew straight home. This tactic minimized the fuel consumed while weaving back and forth thus extending the fighter's escort range. It was also the only way to provide escort all the way to and from the target. As the deep penetration raids flown in 1943 had shown, if the bombers did not have escort all the way to their target, the Luftwaffe would simply wait until the bombers had flown beyond the escort's range and then attack. At first glance this system had the apparent disadvantage of using several times more fighters than necessary for a given mission.
Instead, this relay system maximized escort throughout the entire mission. During the first half of 1944, before it had converted all but one of its fighter groups (the 56th Fighter Group) to P-51s, the Eighth employed three types of fighter aircraft, each with a different range, in relays. P-47s escorted the shallow leg or initial penetration of the mission, P-38s provided the escort on the middle leg, and P-51s flew escort for deep penetration and support over the target. This system proved of special value in February and March when the shorter-range P-47s formed the bulk of the available escort aircraft. Using the P-47, P-38, and P-51 in relays allowed the long-range fighter groups to double the protection of the bombers for a few minutes or enabled one group to leave the bombers five minutes early, drop down to low altitude, and sweep all parts of western, central, and southern Germany.
Until the end of March 1944, RAF Spitfire squadrons supplemented the fighters of Eighth and Ninth by providing the escort for initial penetration and the final withdrawal leg of the heavy bomber missions. With the support from the RAF, the Americans were able to extend the range of their own escort fighters during early 1944 and provide fighter cover all the way to the target. By the end of March, the increase in the number of available American long-range escorts, the decline in the efficiency of the Luftwaffe fighter force, and the Germans' tactic of concentrating their fighter defenses over Germany itself permitted the Americans to release the RAF fighters back to Air Chief Marshal Sir Trafford Leigh-Mallory of RAF Fighter Command. He now regained the use of these resources after having been forced to delay training for ground support for the Ninth and the British 2d Tactical Air Force.
German ground controllers almost never managed to get all the Luftwaffe fighters available to them massed for a single blow, so the Eighth's escort seldom had to deal with overwhelming numbers of defenders. The Germans depended on carefully timed assaults by intact formations to knock down the heavy bombers. A group of Luftwaffe fighters attacking in formation could mass their firepower, downing several aircraft on each pass. However, a relatively few escorts, even if they shot down no enemy fighters, could disrupt the German formations and timing, causing them to lose much of their effectiveness. Even in the worst case, the Germans would have time for only one or two passes against the B-17s and B-24s before escorts arrived. It took brave, determined, and skilled pilots to make a successful solo attack on a heavy bomber formation.
The escort relay system led directly to the increased strafing of German ground targets by US fighters. On 9 February 1944 General Kepner issued the following instruction to his fighter pilots: "Any target of opportunity within the boundaries of Germany can be attacked." With this encouragement individual fighter pilots, high on bravery and low on a sense of survival, began to fly on the deck (very low level) on their return relay flights and to strafe German aircraft, facilities, and other targets of opportunity. To stimulate this practice and to invite the pilots to focus on Luftwaffe fields and facilities, the Eighth began to record official kills for planes destroyed on the ground. In March VIII Fighter Command routinely ordered all fighters to descend to low altitude and conduct fighter sweeps on their return trips. In effect, Doolittle, Spaatz, and Kepner created a system that employed fighters simultaneously in the primary role of escort with a usual and secondary role of ground attack on counterair targets. Because the Germans soon supplied their airfields with liberal amounts of light flak, ground strafing became a battle of attrition on both sides. By then, however, the Eighth had established air superiority over Germany and could afford the losses.
In the relay system, as elsewhere, Ultra and other signal intelligence greatly aided the US fighters' efforts. In March Ultra intercepts revealed the damage done by the low-level fighter attacks. On 8 March Allied intelligence intercepted a Luftwaffe message stating, "the enemy has recognized our own tactics of taking off and getting away from the airfield with all serviceable aircraft before attacks on our ground organization. . . . He has recently put aside a part of the escorting force to attack these aircraft and has achieved successes in this connection." Sixteen days later, as Allied fighter pressure increased, the command organization of the Luftwaffe's home fighter forces reported repeated attacks on aircraft landing on airfields in the home war zone. The report further noted of American tactics: "They imitate the landing procedures of German fighters or effect surprise by approaching the airfield in fast and level flight. The difficulty of distinguishing friend from foe often makes it impossible for flak artillery to fire on them." Given such direct encouragement the Eighth had decided in April to launch pure fighter sweeps in weather unsuitable for bombers to keep up the pressure over western and central Germany. In addition to the ground attack sweeps, the Americans began to launch "free sweeps" toward suspected concentration areas of German fighters to disperse them before they could mount attacks on the US bombers.
Tactical signal intercepts gave further impetus to the new tactics. RAF "Y" Service, a tactical intercept organization, cooperated fully with the Eighth. Upon detecting large concentrations of German fighters assembling to attack the bombers by means of intercepts of in-the-clear transmissions by German ground controllers to concentrations assembling to attack the bombers, "Y" Service vectored groups out on sweeps into the German formations. By the end of March, although the Germans had ceased to use radio telephones, British intelligence had worked out new methods of timing the P-51 sweeps. The British intelligence official history claims that these new methods "contributed a good deal to the Eighth Air Force's success in its policy of deliberately seeking out German fighters and forcing them to accept combat."
The policy of attacking German ground targets took a heavy toll on American fighter pilots, who suffered five times more casualties in strafing than in air-to-air combat with German fighters. By the end of March, Spaatz reported that USSTAF was 500 fighter pilots short of its goal of two pilots per plane, which would allow increased use of the planes without pushing individual pilots to the breaking point. Throughout March and for the rest of the air war against Germany, US fighter escorts accompanied the bombers so efficiently that large US losses resulted only when navigational or timing errors by bombers or fighters caused them to miss their rendezvous, or when a small contingent of the escorts was overwhelmed by large numbers of enemy fighters, which then broke through to attack the bombers.