Der Gabelschwanz Teufel

By Carlo Kopp

[email protected]
[email protected]

Text and Diagrams 1992, 1999 Carlo Kopp, 1999 Corey C. Jordan

 


The contribution of Lockheed's twin-boom P-38 Lightning fighter to the crucial air battles of World War II has been consistently understated for the last five decades. Receiving far less publicity than its single engined stablemate, the P-51, the big twin fought the most important air battles of the 1943 to 1944 period and was a key element in breaking the back of Axis air power over Germany, and in the Mediterranean and the Pacific.

The P-38 excelled in that design parameter which is pivotal to fighting a strategic air war, its combat radius in excess of 700 NM (1) had no equivalent in either camp. The Lightning's combat radius was exploited repeatedly and surprisingly, the Lightning repeatedly succeeded in catching its opponents off guard. Both in the Pacific and the Mediterranean, the P-38 provided long range escort for heavy bombers, long range fighter sweeps deep into hostile airspace and interdiction of surface targets. In the UK, the P-38 wings initially provided long range escort for the 8th Air Force, in that critical phase of the daylight bombing offensive, when Luftwaffe strength was at its best, and US bomber losses began to reach unsustainable proportions. The presence of the P-38 allowed the offensive to continue at a point, where it may have been scaled down due disproportionate attrition.

The Lockheed P-38 was a complex aircraft, using innovative technology, which experienced a painful and protracted development phase and in the end, was denied the credit which it deserved for the importance of its role. This becomes all the more apparent upon closer examination.
 

Early Development - the XP-38 and YP-38


The story of the Lightning began in the mid 'thirties, in a United States still very much isolationist, and in an acquisition climate dominated by fierce rivalry between the Army and Navy, who fought bitterly over what little money was spent on aircraft procurement. There was little support for developing new technology, either from the politicians who saw little payoff in buying toys for the boys, as with senior military officers, most of whom were still thinking in terms of 1920s technology. This now absurd mindset decreed that a single seat fighter was to be restricted to a gun/ammunition load of 500 lbs and a powerplant well below 1,000 HP. At this time, two forward thinking junior officers, Lt. Benjamin Kelsey and Lt. Gordon Saville, realized that a fighter with an air-air weapon load of 1,000 lbs and at least 1,500 HP was both feasible and necessary to defeat the coming generation of long range bombers.

To beat the bureaucracy and circumvent the rules restricting what could be done with fighters, Kelsey and Saville invented the interceptor category and convinced the Army Air Corps to invite submissions on such a design. The February, 1937 Circular Proposal X-608 (ie RFP) for a single and a twin engine fighter called for the use of the very new Allison V-1710 inline liquid cooled V- 12, equipped with the new GE turbocharger for high altitude performance, and for the use of very heavy armament including cannon. Tricycle undercarriage was specified as preferred and large internal fuel capacity was mandatory, to circumvent an administratively imposed ban on the use of drop tanks by fighters.

The single engine fighter contract was won by Bell with what eventually became the ineffective P-39, while the $163,000 AC-9974 twin contract went to Lockheed's Model 22. Lockheed's chief designer, Hall Hibbard, and senior designer, Clarence "Kelly" Johnson, an MIT Master's graduate, had gone through six unorthodox airframe configurations before settling on the twin- boom layout. The XP-38 airframe proposal carried 400 USG of fuel internally, employed a near to symmetrical NACA 23016/4412 section and grossed out at 11,400 lb. Designed for 1,150 HP engines, the Model 22 was built to exceed 360 kts at altitude, stunning performance for the time. Johnson had at the time commented in detail on the possibility of compressibility affecting the handling of the aircraft, this was later to prove to be a major issue.

Construction of the first XP-38 began in July, 1938, while Lockheed was gearing up for mass production of Hudsons for the RAF. Some fabrication problems developed, but these were overcome and the first prototype was loaded on a truck for its journey to March Field on the 31st December, 1938.

The sleek silver prototype was worked on for the following two weeks, and first flew on the 27th January, piloted by Lt. Ben Kelsey, the writer of the initial specification. The first flight was troubled, with severe flap vibration due to a broken support rod, but ended safely, in spite of brake problems. Subsequent flights saw a range of minor problems resolved, as the flight test program progressed.

The XP-38 proved to be a stunning performer, easily achieving 350 kt speeds. The system design of the airframe and propulsion was unique and radical, while strictly functional. The powerplant installation in the nacelle/tail booms exemplified this. The V-1710 engine was mounted in the front of the nacelle, driving a large 3-bladed Curtiss Electric constant speed prop. The GE turbochargers were mounted in the booms, aft of the wing, with intercoolers embedded in the outer leading edges of the wing, ie: The airflow was channeled to the wing-tip via a corrugated double skin and back via the leading edge cavity, and engine glycol radiators in aft boom scoops. The armament of four 0.50 cal machine guns and a single cannon was mounted in the nose, thus avoiding the dispersion problems associated with wing mounted guns.

The test program progressed rapidly and by February, 1939, the flight test team decided to attempt a long range record breaking flight across the continental U.S., in spite of unresolved flap and brake system problems. The attempt ended however in disaster, when carb icing during a prolonged approach at Mitchel Field (2) on Long Island, near the very end of the flight, caused a loss of power. Lt. Ben Kelsey force landed the aircraft on a local golf course. The XP-38 was wrecked, but fortunately Kelsey survived and had successfully demonstrated the superlative speed and range of the aircraft.

The USAAF on the strength of completed tests, ordered thirteen development aircraft, designated YP-38. The Lockheed Model 122-62-02 was fitted with a pair of V-1710-F2 engines rated at 1,150 BHP with GE B-2 turbochargers and weighed in at 11,171 lb empty for a design weight of 13,500 lb. Armament was specified at one 37 mm Oldsmobile M9 cannon, two .50 cal and two .30 cal machine guns. Counter-rotating props were specified, these rotating inboard.

The P-38 was clearly a hot performer and the UK Air Ministry and French AF soon took an interest in the type, seeking a non-turbocharged variant with identical powerplants (and same sense prop rotation) to the Curtiss Tomahawks at that time ordered in significant numbers. Designated the Model 322B and F respectively, the RAF promptly sought a total of 667 of these aircraft, a far cry from the 60 or so which Lockheed expected the US government to purchase. Unfortunately, the buyers did not appreciate the limitations of the V-1710 without turbochargers and Lockheed negotiators accepted the order in spite of the known discrepancy and objections from engineering. This was to have unfortunate consequences at a later stage. The US government also moved to order the P-38, requesting in July, 1939, 66 aircraft.

1940 saw the collapse of France under the treads of Wehrmacht armour, while Lockheed worked away at producing the first YP-38s. The Battle of Britain passed, and much was learned about what was really needed in a fighter, particularly performance at altitude. The first YP-38 flew in September, 1940, soon followed by the development aircraft.

These in turn, were followed by thirty P-38s, armed with four .50 cal machine guns in addition to the cannon, the balance of the initial sixty being made up of the subsequent P-38D.
 

Baptism of Fire - the P-38D and E


Lockheed delivered all thirty P-38Ds to the USAAF by August 1941. The D-model was the first combat capable subtype and was fitted with self sealing tanks, detail aerodynamic changes, Dural bladed props, a low pressure Oxygen system and typically a 23 mm cannon.

The P-38D was followed in production by the P-38E from September 1941 through to April 1942. The P-38E saw further refinements, with a single Bendix 20mm M1 cannon (Hispano) with 150 rpg fitted, changes to the hydraulic and electrical systems, flight instruments and nose undercarriage. In total, 2,000 design changes were carried out to meet the needs of mass production.

The P-38E was followed in production by P-38Fs and RAF spec non-turbocharged 322-Bs, 143 of which were ordered in April 1940 as the Lightning I. The first RAF machines were delivered for testing in March, 1942.

The RAF was unhappy with the 322, as its high altitude performance was inferior to the then current Merlin 40 series powered Spitfire V. The 322 had by that time also demonstrated problems due compressibility in dives which caused 'Mach tuck', a severe nose down pitching moment due to the aft shift of the CoP. This often led to the breakup of the aircraft and usually, loss of the pilot. Like prop rotation sense impaired engine out handling. The 322 affair escalated into a major dispute between Lockheed and the RAF and in the end, all Lightning I airframes were transferred to the USAAF which used them as trainers, under the designation of P-322. The turbocharged Lightning IIs became USAAF production P-38Gs.

Interestingly, the performance problems could have been fixed by fitting Merlins, Lockheed engineers considered this seriously enough to do a paper study in 1941 which indicated that Merlin XX powerplants would provide superior performance, while improving reliability. The US Army however rejected the idea (it has been stated as under the influence of US commercial interests) and thus sentenced the P-38 to engine problems which were not solved until mid 1943.

When the US entered the war in December, 1941, the only serious fighters it had were a mixed bag of P-38Ds and Es, the Curtiss P-40 and Bell P-39 lacked the speed and altitude performance to challenge the Japanese Zero and German Bf109s.

The first Lightnings to see combat operations were the photorecce F-4s of the 8th Photo Group, based in Australia, flying recce sorties over New Guinea and the Coral Sea. Initial deployments of P-38D and E models saw units stationed in the Aleutians and Iceland, with the first combat kill credited to a P-38E in the Aleutians in August 1942, downing a H6K Mavis recce aircraft, soon followed by the killing of a Fw200 Condor off Iceland, by a P-38D.

As the US moved to a war footing, the P-38E was deployed during operation BOLERO to the UK together with later model P-38F aircraft. Initial deployments saw the P-38s fly the Atlantic via Greenland, led by B-17s. After some losses, subsequent aircraft were transported on ships.
 

The Fork-Tailed Devil - the P-38F, G and H

P-38F deliveries commenced in March 1942, this variant being fitted with F-4 model engines rated at 1,225 HP and equipped with pylons for 165 USG drop tanks. Combat flaps were fitted, this facility allowing partial flap deployment at maneuver speeds to increase turn rate. The P-38F was followed in production by the P-38G from August 1942. The P-38G had F-10 engines rated at 1,325 HP, a 300 psi Oxygen system using three bottles in the booms, strengthened pylons for 300 USG drop tanks and a larger combat flap envelope.

The mixed P-38E/F force was deployed to New Guinea, while the UK based aircraft were redeployed to North Africa for the Torch landings. In the Pacific, the P-38 quickly demonstrated its superiority over the A6M3 Hamp (Zero) and Ki-43 Oscar. The P-40's and P-39's suffered heavy attrition in the defense of Port Moresby, and the arrival of the P-38 late in 1942 saw the odds swing in favor of Gen. Kenney's 5th Air Force. The P-38 first engaged the Japanese on the 27th December, destroying 12 aircraft and claiming four probables in a sortie over Buna. By early 1943, several P-38 pilots reached ace status, including Richard Bong, later to become the leading US ace of the war. Equipping the 9th and 39th FS of the 49th and 35th Fighter Groups respectively, these aircraft played a major role in the March 1943 Battle of the Bismarck Sea, stripping the Japanese convoy of its fighter cover.


Lockheed photo

In August, 1942, the Americans landed on Guadalcanal and the P-38 was deployed there soon after with the 13th AF, flying long range fighter missions into the Solomons. Flying from Guadalcanal, in April, 1943, 16 P-38Fs of the 70th and 339th Fighter Squadrons flew 350 NM to Bouganville, at low level, to engage and destroy a Japanese flight carrying Adm Isoroku Yamamoto, Japan's leading naval strategist. In the engagement, Capts. Tom Lanphier and Rex Barber downed two G4M Bettys, (3) one of which contained the Japanese admiral.

The key to extracting range from the P-38 was very much in flying technique, using low RPM and high boost (eg: P-38H 2,300/34 for 215 kt at 146 USG/hr for 600+ NM radius), and until 1944 this was the art of individual units and pilots.(4)

In the ETO, the 8th Air Force was still working up and the bomber commanders initially saw little use for the Lightning, as they still believed in the concept of unescorted daylight bombing. Nearly all P-38F/Gs were deployed to North Africa, to support the Torch landings in Morocco and Algiers.

The P-38s flew air superiority and ground attack missions in the MTO, inflicting heavy damage on the German and Italian air, sea and land convoys attempting to reinforce the theater. The P- 38 was the only US fighter capable of engaging the Bf109G and Fw190A on equal terms, providing escort for bombers well out of the range of the RAF Spitfires. By mid March 1943, the Axis had a force in excess of 500 Ju-52s, Me-323s and SM.82s dedicated to reinforcing the theater. The Allies applied the long-legged P-38 to cut this air bridge from Sicily, some measure of the intensity of this battle can be gauged by three notable sorties. On the 5th April 26 P-38s engaged a convoy of 70 Ju-52s escorted by 24 Luftwaffe fighters, destroying 11 transports and 2 fighters, for the loss of 3 P-38s. On the 10th April, 41 transports and 8 fighters were dispatched, the following day 26 Ju-52s and 5 fighters were destroyed for no loss. The Allied landings in Sicily and Italy saw further successes for the P-38 force, a notable highlight being an Allied convoy escort CAP on the 9th October, during which Lt.Col. W.L. Leverette killed 7 Ju-87 dive bombers, another of his pilots killing another 5 aircraft. It is not surprising that German pilots nicknamed the P-38 Der Gabelschwanz Teufel (the Fork-Tailed Devil).

The outstanding success of the P-38 in the Med and the Pacific was not matched by units of the 8th AF in the UK. These were applied to the long range escort role, equipped with the P-38H. The H model, a stopgap while production of the P-38J was being organised, supplanted the G in May, 1943, and differed primarily in the use of more powerful F-17 engines with automatic engine mixture controls (autolean/autorich), B-33 turbochargers and automatic oil cooler flaps, and a new AN-M2C cannon. The more powerful V-1710F-17 hit the design limits of the leading edge intercoolers, oil coolers and radiators, which limited military power output to 1,240-1,350 HP, only late build aircraft with improved oil coolers could maintain the nominal 1,425 HP.

The 55th FG became operational with the P-38H at Nuthampstead in the UK, in October, 1943, deploying from McChord Field in Washington state, where it was a training unit periodically stripped of squadrons to reinforce MTO and SWPA FGs. Tasked with bomber escort at high altitude, the single group of P-38s provided deep escort outside of the range of the seven P-47 groups and numerous RAF Spitfire squadrons, which escorted bombers over the Channel. At this time the Luftwaffe was at its peak, with 8 JagdGeschwaders (JG1, JG2, JG3, JG11, JG26, JG51, JG106) equipped with Bf109G and Fw190A and 3 NachtJagdGeschwaders (NJG1, NJG2, NJG6) equipped with Bf110G available to defend the continent, each JG/NJG with typically 3 Staffels (Squadrons) per JG/NJG.

The P-38s were all that stood between the Luftwaffe and the bombers, 500 NM deep inside hostile airspace. Unescorted, the B-17s and B-24s suffered up to 30% attrition on some raids and the P-38s were the only aircraft with the radius to the task. Typically, P-47 Thunderbolts provided fighter cover to and from the German border. The P-47, truly an excellent high altitude fighter, was saddled with its limited range. They were just beginning to be equipped with belly mounted drop tanks. Yet, these were still inadequate for flying beyond the German frontier. The rotund Thunderbolt would suffer from a lack of range until the arrival of the P-47D-25-RE later in 1944. This model had 100 gallons of increased internal tankage and provision for three external drop tanks. Even with the arrival of some P-51B Mustangs, the P-38 was to bear the brunt of deep penetration escort duty for the next several months. The P-51B equipped 354th (9th AF) went operational in late December, 1943, followed by the 357th and 4th FGs in February, 1944. The P-38 equipped 264th went operational in March, 1944, and the 479th as late as May 1944. During the critical late months of 1943 the P-38 stood alone, with Mustang numbers building rapidly from February 1944. 

With a large proportion of Pacific and Med P-38 operations flown at medium to low altitudes, Lockheed and Allison had little operational experience with the aircraft at high altitude and low ambients and this was quickly revealed. The Allisons misbehaved quite consistently, 'throwing rods, swallowing valves and fouling plugs' while the intercoolers often ruptured under sustained high boost, and turbocharger regulators froze at 10 in. or 80 in. of boost, the latter often resulting in catastrophic failures. Even with the arrival of the P-38J, engines and turbochargers continued to fail. The new intercooler/oil cooler design was actually too efficient and the enlarged radiators became a new problem. Fuel too, was a source of trouble, it is believed by many knowledgeable people that the majority of fuel used in Britain was improperly blended, the anti-knock lead compounds coming out of solution (separating) in the Allison's induction system at extreme low temperatures. This could lead to detonation and rapid engine failure, especially at the higher power settings demanded for combat.

Many of the P-38's assigned to escort missions were forced to abort and return to base. Most of the aborts were related to engines coming apart in flight. The intercoolers that chilled the fuel/air mixture too much. Radiators that could lower engine temps below normal operating minimums. Oil coolers that could congeal the oil to sludge. These problems could have been fixed at the squadron level. Yet, they were not. It took the P-38J-25-LO and L model to eliminate these headaches. Add sub-standard fuel, green pilots, poor tactics and the 8th had a serious problem in the making. Having had their numbers seriously reduced by aborts, the remaining fighters were all the more hard pressed by vastly superior numbers of Luftwaffe fighters. The single inexperienced 55th FG often fought the JGs outnumbered 5:1, and the operational debut of the 20th FG in late December 1943, equipped with a mixed inventory of P-38H and P-38J-5/10-LO did not dramatically improve the situation.

There is little wonder that loss rates were relatively high and the kill to loss ratio was below that of the P-47's which could be massed by the hundreds (700 P-47's flying escort was not uncommon). The Luftwaffe quickly learned to position the bulk of their fighters just beyond the range of the Thunderbolts and repeatedly flew aggressive small unit ambushes against the handful of P-38s tied to close escort and thus denied the freedom to engage at will.

To aggravate these problems, inadequate cockpit heating resulted in severe pilot frostbite, while the Luftwaffe quickly learned about the compressibility problems in dives, with German pilots evading the P-38s by executing a split-S at high speed. The initial roll rate was not spectacular and the easily recognized planform provided the Luftwaffe with yet another advantage to play.

Poor serviceability and engine problems meant that initially 50 or less aircraft were available for such missions, including the first escorts over Berlin, and therefore the 55th and later also 20th FG usually fought the JGs outnumbered between three to one and five to one, as noted previously. The large number of engine failures deep inside enemy airspace exacerbated the problem, and the aggregate exchange rate, accidents inclusive, dropped to about 1:1.5 in favour of the Lightning by 1944. Aircrew morale dropped, moreso due to the large number of single engine landing accidents, thus further damaging the aircraft's reputation. The technical problems were not resolved until the introduction of the P-38J-25-LO, by which time the 8th had decided that the new Merlin powered P-51B/C was a better choice for the mission.

In hindsight, while the P-38H and early J variants may not have performed to expectations in the ETO, what is overlooked is that their presence alone allowed the daylight offensive to proceed at the most crucial phase of the battle, the last quarter of 1943, leading to eventual air superiority by the middle of 1944, when the P-51's reached full strength. It is safe to say that were larger numbers of the P-38 available to offset Luftwaffe numbers, and more experienced pilots made available to crew the P-38, the overall result would have looked far better.

The common conclusion that the P-38 was inadequate for the needs of the 8th is frequently based upon comparisons of the scores achieved by the 20th and 55th FGs during the late February "Argument" raids, in comparison with the P-51B equipped 354th FG (9th AF) and the 357th FG (8th AF), and the scoring performance of the P-51B equipped 4th FG in the early March raids into Germany. The factor which is ignored by critics of the P-38 is tactical and aircraft/powerplant handling experience. The 4th FG comprised the former RAF Eagle Spitfire squadrons, and was by far the most experienced USAAF FG in the ETO. The 354th was being led by Blakeslee, formerly of the 4th FG. The 357th drew directly on the experience of the 4th and the 354th FGs. All three FGs drew on the initial long range escort experience of the 55th.

In summary a valuable pool of tactical experience and engine handling experience for the Merlin equipped P-51B existed in the 4th FG, and this experience could be directly applied to the P-51B. No such experience existed for the turbocharged Allison powered twin engined P-38 in theatre. The valuable tactical and handling experience of the SWPA FGs was a theatre away. Only a limited number of MTO pilots were made available for the 20th and 55th, and both units had taken heavy losses during the early escort missions, impacting both morale and the rate at which experience could be accumulated in these FGs. Many of the P-38 handling techniques developed in the SWPA to counter the highly manoeuvrable and skilled Japanese opposition, such as differential throttle and rudder assisted roll entries, were never practiced widely in the ETO.

Despite these difficulties the 55th did well on a number of sorties during this period. On the 3rd November, 1943, the 55th in concert with the experienced 4th, 56th and 78th FGs clashed with the elite JG 1. The 55th accounted for 7 Luftwaffe fighters of the 13 claimed. On the 25th November, 1943, 4 FW-190s were claimed for the loss of one P-38H, one of the Focke-Wulfs belonging to Major J. Seifert (an "expert" with 57 kills), Gruppenkommandeur of II/JG26. Other sorties were much less successful, and heavy losses were suffered on a number of occasions. A heavy price was exacted for the deployment of inexperienced pilots in a very demanding theatre in the hitherto untried long range escort mission profile.



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