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The Lockheed XP-58 Chain Lighting was a two-man version of the P-38 that suffered from repeated changes of purpose, and that never entered production.
Early in 1940 Lockheed needed War Department permission to export a version of the Lightning to the British and French. In return they agreed to develop an advanced version of the P-38 at their own expense. In the end Lockheed paid for most of the costs of the first prototype, apart from $451,556 to cover changes ordered by the Government, and the Government provided almost $1,900,000 for a second prototype that was ordered but never built.
The initial design was for a one or two seat aircraft, to be powered by two turbo-supercharged Continental IV-1430 liquid cooled engines. In May 1940 the Air Corps decided that work should focus on the two-seat version, which became the XP-58.
The development of the new aircraft was hindered by a constant stream of changes to the specification.
In July 1940 it was decided that the Continental engines weren’t powerful enough, and a pair of 1,800hp Pratt & Whitney XH-2600-9/ -11 engines were chosen instead.
Lockheed issued a revised specification on 10 September 1940. As well as the new engines, this version had a second 20mm cannon in the nose, along with the standard four 0.5in machine guns. Plans to fit guns in the rear of each boom were dropped in favour of using a remote control Air Arm dorsal turret carrying two 0.5in machine guns. This version of the aircraft was 45% heavier than the original design, and almost 50mph slower, with a top speed of 402mph.
In October Pratt & Whitney announced that they were cancelling the XH-2600 engine. Lockheed had to find a new engine, and looked at the Lycoming XH-2470, the Continental XH-2860 and the Pratt & Whitney R-2800. Lockheed preferred the Pratt & Whitney engine, which they estimated would give a top speed of 418mph. The Air Corps didn’t approve, and suggested the 2,350hp Wright XR-2160 Tornado instead.
In March 1941 the Air Corps officially put its support behind the Tornado powered version.
In May 1941 the Air Corps ordered Lockheed to add pressurized cabins for the two crewmen, at government expense, and to add a second remotely controlled turret, in the ventral position. However they still wanted a top speed of 450mph, despite yet another increase in weight. The prototype was to be completed by August 1942.
In December 1941 the American entry into the war saw a major reduction in the priority allocated to the P-58. The design team dropped from a peak of 187 in October 1941 to a low of 12 early in 1942! However at this stage the aircraft was well ahead of the troublesome Tornado engine. Despite these problems, in May 1942 a second prototype was ordered! This aircraft was to have more fuel capacity, giving it double the range of the first prototype.
1942 also saw the USAAF struggle to decide what they wanted the P-58 to actually be. This began with a suggestion to change the forward guns to one 75mm cannon and two 0.5in machine guns. This meant it would no longer be suitable for use as a long range escort fighter. Studies were carried out in using it as a two-seat attack aircraft with six forward firing 20mm cannon or a three seat attack/ bomber with an internal bomb bay, a bombardier’s position in the nose, and possibly still with the 75mm cannon. However by 1942 the USAAF already had good low level and light bombing aircraft, so the P-58 wasn’t needed in those roles.
In November 1942 Lockheed were ordered to complete the prototypes as bomber destroyers. The first was to carry four 37mm forward firing cannon, the second one 75mm cannon and two 0.5in guns. Both would keep the dorsal and ventral turrets and the turbosuperchargers. Although this seemed like a useful design in 1942, by the time it would have entered production, neither Japan nor Germany had any effective strategic bombing forces, so it would have rather lacked purpose.
In January 1943 Lockheed suggested that only one prototype should be completed, with an interchangeable nose that could be used to test the different armament layouts.
In February 1943 the Tornado engine programme was cancelled, forcing yet another change of engine. This time Lockheed picked the turbosupercharged Allison V-3420-11/ -13 twenty four cylinder liquid cooled engine, rated at 2,600hp at take off and 3,000hp at 28,000ft. This would be the engine used by the prototype when it actually took to the air.
The sole prototype, with dummy turrets and no forward firing guns, made its maiden flight on 6 June 1944. Lockheed carried out 25 test flights, before the prototype was finally delivered to the USAAF at Wright Field. By this point the USAAF had no use for the P-58, and in early 1945 it became a non-flying instructional airframe.
Engines: Allison V-3420-11/ -13 twenty four cylinder liquid cooled engine
Power: 2,600hp at take off, 3,000hp at 28,000ft per engine
Crew: 2
Wing span: 70ft
Length: 49ft 5.5in
Height: 16ft
Empty weight: 31,624lb
Loaded weight: 39,192lb
Maximum weight: 43,000lb
Maximum speed: 436mph at 25,000ft
Cruising speed: 283mph
Rate of climb: 2,582ft/ min
Service ceiling: 38,200ft
Normal range: 1,260 miles
Maximum range:2,650 miles
Lockheed Aircraft Since 1913, René J Francillon