In the early months of 1940, America's entry into World War II was still
nearly two years away. But on the European continent, nothing seemed to be
able to slow the onslaught of the German military as one country after
another came under Nazi control. It appeared to be only a matter of time,
and perhaps a very short time, before England would be facing the German war
Great Britain needed the weapons and materials of war in great quantity, and
it needed them quickly. Nothing was of higher priority than fighter planes
to defend the island nation, and in January 1940, before the fall of France,
the Anglo French Purchasing Commission came to America hoping to acquire
additional P-40s. But the Curtiss production lines were operating at
capacity, so some "back room" discussions sent them to see James H. "Dutch"
Kindelberger, the president of North American Aviation.
The British had purchased aircraft from North American before, but they had
been trainers, not the fighters they now so desperately needed. In fact, up
to that time, North American had never produced a true fighter design.
During World War II, it would later become common for one company to produce
another's design. Vega and Douglas would build Boeing's B-17, Goodyear would
build Vought's Corsair, General Motors would build Grumman's Wildcat and
Avenger, and Curtiss would even build Republic's Thunderbolts. But in 1940,
North American was not interested in producing Curtiss P-40s for the
Instead, North American informed the British that it could produce an even
better fighter plane than the P40 while still using the same Allison V-171 0
inline engine. Reports have been published stating that North American
stipulated in the contract that this would be accomplished in only 120 days,
but in fact, there was no such guarantee in the contract. Nevertheless,
North American did assure the British that the plane could be designed and
produced very quickly.
On April 10, 1940, the proposal was accepted, and the
prototype, assigned North American's model number NA-73, was ordered. The
following month, France fell to the Germans, and England was indeed alone.
Soon, a small number of Spitfires and Hurricanes would begin the defense of
England against the Luftwaffe in the Battle of Britain. Britain's need for
fighters was never more desperate.
Asked to name
the American military personnel who made significant contributions to
victory in World War II, men like Dwight Eisenhower, George Patton, Douglas
MacArthur and Chester Nimitz would be on most lists. But a very good
argument could also be made to include First Lieutenant Benjamin S. Kelsey.
Lt. Kelsey was head of the Army Air Corps Pursuit Projects Office at Wright
Field, and he was the single most important man in the acquisition of what
would eventually become the P51 Mustang fighter. With a degree in
aeronautical engineering from M.I.T., Kelsey was qualified in aircraft
design and performance, and he ingeniously found the means and the money to
keep the program going until America's entry into the war ensured its
On May 4, 1940, when North American obtained release to sell the NA-73 to
the British, Kelsey had included the stipulation that two aircraft from the
first production batch would be turned over to Wright Field for testing.
This meant that the British would buy the U.S. Army two aircraft which it
did not then have the funds to purchase for itself.
Kelsey also knew of the National Advisory Committee on Aeronautics' (the
forerunner to NASA) studies on the laminar flow airfoil, and as an
aeronautical engineer, he understood its importance to new aircraft design
and performance. As a result, NACA's Eastman Jacobs was assigned to North
American's team that was working on the new fighter for the British. Raymond
H. Rice was North American's chief engineer, Edgar Schmued their chief of
design, and Ed Horkey was the aerodynamicist. Along with Jacobs, they worked
day and night, seven days a week, to produce the new fighter as quickly as
Curtiss had been ordered to turn over its design studies and other pertinent
information on the XP-46. This included the radiator scoop originally
intended for installation under the fuselage of the P-40. This scoop, which
provided cooling air for glycol and oil cooling, was also to have a hot air
exit ramp which would create thrust that more than offset the drag caused by
the frontal cross-section for the scoop. Though never fitted operationally
to the P-40, it held promise and was one of the features incorporated in the
design of the NA-73. Just how much the data from Curtiss was used is subject
to debate. Curtiss engineers state that it was almost total, while those at
North American claim that little of the information was used. The truth is
probably somewhere between these two extremes. Clearly, the NA-73 had a lot
in common with the XP-46, and a rational analysis would indicate that the
NA-73 could not have been engineered in such a short period of time without
considerable use of the Curtiss data. But equally as clear is the original
thinking added by the North American design team. Among the most important
changes was the addition of the laminar flow wing.
On September 9, 1940, only 102 days after the contract had been signed, the
NA-73X prototype was rolled out though still waiting for its engine. The new
fighter was named Mustang by the British, and the first British version was
designated Mustang I. As soon as it was available, the 1,120hp Allison V-171
0-39 powerplant was installed, and engine and taxi tests began. On 26
October, Vance Breese lifted the aircraft off the runway for a maiden
flight. Testing continued until Paul Balfour was forced to make a deadstick
landing. The NA73X flipped over on its back, and it took six weeks to make
repairs and get the aircraft ready to fly again. The first production
Mustang I soon joined the repaired prototype in the test program, and
shortly other Mustangs were heading for England.
the evaluation of the flight test aircraft showed that the NA-73 was indeed
superior to the P-40 Warhawk which was considered to be the best
single-engine fighter in the U.S. Army Air Corps inventory at the time. A
lot of criticism has been written about the AAC's initial lack of interest
and subsequent slowness to act concerning acquiring Mustangs for its own
use. This simply is not so. All evidence is to the contrary, particularly
considering the political and economic situation in America at that time.
Here again Lt. Benjamin Kelsey was the man who deserves the credit.
As stated earlier, Kelsey saw to it that two aircraft from the original
British order were supplied to Wright Field for testing, but his efforts did
not stop there. Kelsey was able to place an order for 150 P-51s on July 7,
1941, and this was before the first XP-51 even arrived in Ohio. It was a
small order for the first U.S. version, but it was all that funding would
allow at that time.
The P-51 was very similar to the Mustang I, with the main difference being
the replacement of the mixed machine gun armament of the British version
with four 20mm cannon. Clearly, the USAAC had a genuine interest in the
NA-73, even before it had a chance to obtain one. The situation in Europe
would cause 93 of the P51s to be sent to the Royal Air Force where they were
called Mustang IAs.
With an order from the U.S. Army, North American chose the nickname "Apache"
for the U.S. aircraft. But by then the British name, Mustang, had taken
root, and it became the official nickname of the USAAC.
With no funds available for pursuit aircraft, as fighters were then called,
Lt. Kelsey came up with a way to beat the system and get some additional
Mustangs on order for the USAAC. Using some remaining funds for attack
aircraft, Kelsey asked North American to develop a dive-bomber version of
the NA-73. Choosing A-36, which was the next available attack designation,
Kelsey ordered 500 of these dive-bomber versions on April 16, 1942.
Ironically, the North American name, "Apache," was commonly used with the
A-36 but never officially recognized by the newly renamed U.S. Army Air
About a month and a half after the order for 150 P-51s had been made on July
7, 1941, the first XP-51 arrived at Wright Field on August 24. The second
did not join the first until December 16. In between these deliveries, the
Japanese had caused everything in the United States to change with their
attack at Pearl Harbor. No one could claim any longer that this was Mr.
Hitler and Mr. Churchill's war. It was World War II.
In numerous accounts about the development of the Allison-powered Mustang,
it has been stated that its poor performance at high altitudes was a
surprise and a disappointment to the British and to the USAAF as well. This
simply is not so. The aircraft designers of that day had more than
sufficient knowledge of powerplants, and they were capable of determining
that the Allison engine and supercharger combination installed in the
aircraft would have a drop in performance above 15,000 feet. Clear evidence
of this is that two of the P-51s, ordered even before the flight of the
first XP-51, were reserved for testing with a Packard-built Rolls Royce
Merlin engine. They knew that the Allison-powered Mustangs would be low-Ievel
fighters, while the Merlin-powered aircraft would be the high-altitude
versions. By comparison, Mustangs with the Allison engine could outperform
the Merlin-powered variants below 15,000 feet, but no writer has criticized
the P-51B, -C, -D, or -K for having less performance at low altitudes. It
has been claimed that the Merlin engine is what allowed the Mustang to reach
its potential. If only high-altitude performance is considered, this would
be true. But a more correct assessment would be that both the Allison and
Merlin-powered versions performed very well at the altitudes where they were
designed and intended to operate.
P-51B AND -C
The first production version of the Mustang to be equipped with the Merlin
engine was the P-51B. Identical airframes were produced at North American's
Dallas plant and were designated P-51Cs. By the time these variants were
ordered, America was in a full wartime economy, and production numbers of
these Mustangs were in the thousands instead of the hundreds. The British
received these two variants as well and named them Mustang Ills. Seventy-one
P-51Bs and twenty P-51Cs were fitted with cameras and designated F-6Cs.
second half of 1942 and much of 1943, U.S. heavy bombers suffered great
losses as they flew unescorted, daylight missions over enemy territory. The
new, high-altitude versions of the Mustang have been heralded as the savior
of the bombing campaign. But it must be understood that the reason the
bombers were not escorted by fighters during the early months of America's
involvement in the European theater was a matter of choice and not because
of a lack of adequate fighters.
When he was in command of the 8th Air Force, General Ira Eaker did not
believe the bombers needed escort. He thought that the bombers' defensive
armament would be protection enough. High rates of losses never deterred him
from this belief. Accordingly, Eaker turned down the P-38 Lightnings
provided him to protect his bombers. The P-38s, with enough range to escort
the bombers to any of their targets, spent time in England with relatively
little to do, and many were subsequently sent to Africa.
By mid-1944, P-51 Mustangs were fast replacing other types of fighters in
the USAAF. The early variants with Allison powerplants were combat veterans
and had proven to be superior in performance over any other allied fighter
below 15,000 feet. The Merlin-powered P-51B and P-51C possessed outstanding
high-altitude performance that made them formidable adversaries to any enemy
aircraft above 12,000 feet. Additionally, all Mustang variants had great
range capabilities which exceeded most other fighter aircraft of World War
P-51D AND -K
But as good as the Mustang was, there were several problems with the design,
and complaints about two shortcomings in particular resulted in the
development of the P-51D and subsequent versions. First, the visibility from
the original standard canopy was very restricted. In combat, the pilot who
saw his adversary first had a decided advantage, and more often than not,
the first indication a fighter pilot had that he was under attack was the
impact of bullets on his aircraft. Although the British Malcolm canopy had
been fitted to many early Mustangs, it was an interim solution which was not
available in sufficient quantities for all aircraft.
complaint about the Mustang that required correcting was that the four
.50-caliber machine guns were not sufficient for the average pilot. Further,
they were subject to jamming, and this was due in part because they were
mounted at an angle.
To correct the visibility problem, two P-51Bs were modified with a cut down,
aft fuselage section and a full bubble canopy. This provided excellent
visibility all around and above the aircraft. Beginning with the P-51D and
the nearly identical P-51K, all future Mustang variants were designed and
fitted with full bubble canopies.
For more firepower, the number of machine guns was increased from four to
six. This was a rather simple matter because the gun bays in previous
Mustangs had always been large enough for an extra gun in each wing. To
reduce chances of jamming, the guns were mounted upright instead of at a
slant. Additionally, they were installed along the dihedral of the wing
rather than being parallel to the ground line as they were in earlier
variants. The P-51D and all subsequent production versions had six internal
machine guns. Ammunition capacities for the guns were also increased, and a
K-14B gyro-computing gunsight replaced the reflector sights during the P-51D
During the second half of 1944, P-51Ds and P-51Ks were arriving in both the
European and Pacific theaters in considerable numbers. Although they served
in combat during World War II for less than a year, their numbers exceeded
all previous versions combined. They scored impressively against all types
of enemy aircraft, although admittedly, the German and Japanese air forces
were significantly reduced in both quality and quantity during the last 12
months of combat.
Even the early versions of the Mustangs were considered to have substantial
eye appeal with their sleek aerodynamic lines, due in part to the
streamlined nose which housed the inline, liquid-cooled engine. But with the
introduction of the bubble canopy on the P-51D and P-51K, there were few who
would argue that these Mustangs were not among the most handsome fighter
designs ever produced. This undoubtedly lead to the Mustang's overall
popularity among pilots and aviation enthusiasts alike.
In the air, the Mustang could hold its own against any other
propeller-driven aircraft of World War II. But in the closing months of the
war, particularly in Europe, there were decreasing opportunities for aerial
combat with enemy fighters. Instead, Allied fighters were used more and more
for strafing missions against the German army on the ground, airfields, rail
yards and other ground targets. These were usually well defended by a
considerable number of antiaircraft weapons ranging from machine guns to the
famous German 88mm gun. A single hit to the liquid cooling system would
bring a Mustang down, and because the critical components of this cooling
system were in the forward and lower sections of the fuselage, the Mustang
proved more vulnerable to ground fire than it was to enemy aircraft. As a
result, the ratio of losses to missions flown was higher on these ground
attack missions for the P-51 than they were for the P-47 Thunderbolt with
its air-cooled engine. The vulnerability of the liquid-cooled engine to
ground fire would surface again as a problem for the F-51D in Korea where
losses were very high.
The P-51D and the very similar P-51K
became operational in considerable numbers during the final year of World
War II, and they were the final Mustang variants to fly combat missions in
that war. Although the production lines had already begun deliveries of the
P-51H prior to the end of hostilities, none reached operational units in
time to participate in combat. Because it was considerably lighter, the
P-51H offered a significant increase in performance over the P-51D and
P-51K, and the center of balance problem was finally corrected. In the early
post-war years, the P-51H became the Mustang of choice for the USAAF and
then the USAF, while the P-51Ds were the first to be turned over to the Air
National Guard. But as the new jets replaced more and more propeller-driven
fighters, even the P-51Hs were sent to Guard units.
The P-51H, which first flew on
February 3, 1945, may appear to be nearly identical to the previous P-51D.
However, the fuselage, wing and tail section were all redesigned. Even the
main landing gear was changed from that on all previous Mustangs. This
redesign was accomplished in order to correct some balance problems as well
as to lighten the airframe and thereby improve performance. Both empty and
gross weights of the P-51H were 500 pounds lighter than the P-51D, and
maximum speed increased between 50 and 86mph depending on altitude and the
configuration of the aircraft. The lines of the P-51H were cleaner, and even
the exhaust shroud was more streamlined in order to reduce drag.
The Packard Merlin V-1650-9 engine was equipped with water injection to
provide in excess of 2,000hp in a wartime emergency. The standard dry rating
was 1,380 horsepower. The engine turned an Aeroproducts A-542-B1 or B2
uncuffed propeller which was 11 feet 1 inch in diameter.
With a top speed of 487mph in a clean configuration, the P-51H was the
fastest propeller-driven aircraft produced during World War II. However,
production was so late that the war ended before any of these hot-rod
Mustangs saw combat service. At the end of the war, defense orders were cut
across the board, and the P-51H was no exception. The initial order of 2,000
aircraft was cut to just 555 examples. In addition to being faster in the
air, improvements were made to make the P-51H easier and faster to maintain
on the ground. The internal armament of six .50-caliber machine guns was
retained, but the ammunition was loaded in removable boxes that made
rearming the weapons much simpler and quicker.
As World War II ended, the P-51H began replacing P-51Ds in regular Air Force
squadrons, and the older versions were passed on to the Air National Guard,
bulldozed into the ground, or cut up and burned without ever returning back
to the U.S. at war's end. As excellent as the performance of the P-51H was,
its days of service with the regular Air Force were limited as the F-80s,
F-84s and F-86 jet fighters began to take their place on the flightlines.
The P-51H followed the D into the Guard units but were retained there for
even a shorter time than many of the older versions.