B-40 Flying Fortress

The B-40 Flying Fortress was a long-range bomber developed by Lockheed Vega based on a long-range Boeing B-17 bomber. At the beginning of the Second World War, the US Air Force did not have fighter aircraft that had enough flying range to accompany the bombers. Large losses during the first raids led to attempts to create escort fighters based on heavy bombers. As one of the most massive bombers, the B-17 also did not escape such experiments. Such a plane was created under the designation YB-40, based on the B-17F to provide additional firepower to protect heavy bomber formations.

The 1930’s saw bombardment rocket into a position of almost exclusive importance, while pursuit aviation fell into a limited and narrowly defensive role. This was partly theresult of the technological advances in bombardment and partly of the growing influence of the Mitchell–Douhet doctrine.” Heavily armed, formations of high speed bomberswere considered virtually invincible.

By 1939, General Arnold and other bomber advocates were beginning to question the invincibility of self–protecting bomber formations. They had received foreign reports where bombers were experiencing losses to pursuit. In particular, the Spanish Civil Warproved to Arnold that pursuit aircraft could indeed cause heavy losses to unescortedbombers. A Russian report, for example, stated that: “Enjoying greater speed andmaneuverability than bombing craft, as well as greater ceiling, the pursuit craft alwaysfound themselves in a favorable position in aerial combat and were quite successful in theiraction against bombers.”

In August 1942, the AAF contracted with Vega Aircraft Corporation to modify the second production B-17F to become the first XB-40 ('X' for experimental) and later renamed the YB-40 ('Y' for service test) gunship. Initially, the AAF ordered thirteen 13 YB-40s. The first prototype XB-40 was manufactured in November 1942 by Vega. As the basis of the new aircraft, the finished standard B-17F-1 (serial number 41-24341) manufactured by the Boeing plant was taken.

Modifications included converting the bomb bay into an ammunition magazine and installing additional armor plating to protect the various crew positions. The YB-40 could carry nearly triple the amount of ammunition - 11,200 rounds as compared to 3,900 rounds carried on a B-17F. Additional modifications included adding a chin turret with two .50 caliber light-barrel machine guns, replacing the single .50 caliber waist guns with staggered, twin-mounted emplacements and most notably adding a second manned dorsal turret installed in the former radio compartment. The nasal unit had remote control from the plexiglas nose.

The YB-40 had 18 or more guns as compared to only 13 guns on the standard B-17F. Single Colt-Browning M-2 in the side embrasures were replaced by paired ones. In addition, the aircraft retained the standard B-17F armament (a superfacial, a ventral ball and tail turret with a pair of 12.7 mm M-2 machine guns in each), which resulted in full protective weapons up to fourteen 12.7 mm machine guns. For the best protection of the crew and engines, additional armor was established. The plane did not carry a bomb load. Instead, the bomb bay of the aircraft was adapted to store additional ammunition. The normal ammunition of all machine guns was 1,135 cartridges, which could be increased to 1,765 cartridges by reducing the fuel reserve on board.

The first flight of XB-40 took place on November 10, 1942. Similarly, twenty B-17F (the Vega-built aircraft of the later series) were converted. The aircraft received the designation YB-40. In addition, four TB-40 training aircraft were built (also a modification of B-17F). Although the project had the designation Vega (Project V-139-3 for XB-40 and Project V-140 for YB-40), due to Vega's higher priority tasks, the refitting of all machines was carried out at the Douglas plant in Tulsa ( Tulsa, Oklahoma. The first YB-40 was manufactured in February 1943. During the construction, many different weapon configurations were tested. Some YB-40s were equipped with turret mounts in the bow and tail with four 12.7 mm Colt-Browning M-2 machine guns. Some aircraft tested the installation of 40-mm guns and the installation of as many as 30 machine guns of various calibers in numerous nests in the tail section and in additional turret installations above and below the fuselage. Unfortunately, not a single photo of YB-40 with 30 machine guns was preserved.

In April 1943, twelve YB-40 arrived at the RAF base in Alconbury and joined the 327th Bomber Squadron of the 92nd Bomber Group to conduct operational combat tests. A total of thirteen YB-40 planes were sent, but one of them (pilot Lt. Kasey (Casey)) made an emergency landing in Scotland due to a lack of fuel.

The USAAF Leadership hoped that a ratio of one YB-40 to two or three B-17s would provide enough protection within the bomber formations for the upcoming raids into Germany. The YB-40s flew their first operational mission on May 29, 1943 in an attack against submarine pens and locks at Saint-Nazaire.

The leadership quickly discovered that the YB-40s were unable to keep up with the B-17s, especially on the return from the target after the formation dropped their bombs. The YB-40s became more of a burden than a help to the formation as they fell behind. The YB-40s were nearly 4,000 pounds heavier than the standard, fully armed B-17. The additional armor on the YB-40 added nearly an additional ton to eachplane; after bombs were dropped, the lighter B-17s increased speed and the YB-40s couldnot keep up. In addition, such a "fighter" was not sufficiently maneuverable. Thus, the YB-40 could defend only itself, and not accompanied bombers.

Also, the YB-40 had significantly greater aerodynamic drag due to the additional gun stations. As a comparison, it took the B-17F only 25 minutes to climb to an altitude of 20,000 feet while it took the YB-40 48 minutes to climb to the same altitude. After participating in only ten missions, in August 1943, the YB-40s were withdrawn from service. A few months later, the first long-range fighter escorts with the P-51B and later P-51D Mustang began operations in Europe and eventually neutralized German fighters.

It was recognized that the YB-40 project did not justify itself. On 10 June 1943, the Combined Chiefs of Staff issued a directive known asPOINTBLANK, which put German fighter strength at the top of target list all in acategory of its own. The Americans welcomed the POINTBLANK directive because it shifted bombing from submarine pens towards “defanging” their arch enemy the Luftwaffe.

The surviving YB-40 were retrofitted to the standard configuration of the B-17F or used in the US as simulators for shooting. While the YB-40 concept proved a failure with the aircraft being too heavy and slow, the crews from the 92nd Bombardment Group provided some valuable lessons from the operational testing of the YB-40s. These lessons led to modifications conspicuous to the final production variant of the B-17 bomber, the B-17G as well as to the late production B-17Fs. These B-17s incorporated the chin turret, the offset waist gun positions which allowed for greater freedom of movement, and an improved tail gunner station with much larger windows. As a result, the later production B-17Fs and B-17Gs were more effective in defending themselves.