A tantalizing concept that did not live up to initial expectations, the heavily armed bomber escort version of the Flying Fortress was tried in combat over Europe.
When early Army Air Forces notions of unescorted bomber formations proved unsustainable in the face of aggressive German fighter attacks, American responses centered on developing fighters with greater range to protect the bombers, and limited tests of converted bombers as gunships to be placed at strategic locations within a bomber formation.
Much as naval vessels serving as escorts contribute to an umbrella of antiaircraft coverage over a task force at sea, escorting gunship versions of the B-17 were seen as one answer to the scourge of German fighter attacks.
A B-17 bomber escort variant, the XB-40, showed initial promise. A similar project with a B-24D converted into the XB-41 escort never developed beyond stateside testing.
Lockheed’s Vega plant embellished work already done to a B-17F at Cheyenne, Wyoming’s Fortress modification center, where a boosted power tail gun mount and a dummied-in Bendix chin turret had been installed. A second top turret, built by Martin, was added in the radio room area of the B-17. This quirkily gave the B-40 one Sperry upper turret and one Martin upper turret. The waist gun mounts were given two instead of one machine gun each.
The resulting XB-40 carried much more .50-caliber ammunition in its bomb bay. Altogether, 24 B-17s were earmarked for the B-40 program. The XB-40 was followed by 19 service-test YB-40s intended to test the concept in combat, plus four TB-40s that became trainers.
Where many combat B-17s ultimately carried about 4,000 to 5,000 rounds of ammunition, the service-test YB-40 could carry as much as 17,000 rounds for short missions, with a normal load of more than 11,000 rounds for longer sorties.
At Eglin Army Airfield’s proving grounds in the fall of 1942, the XB-40 could not quite reach 300 miles per hour, topping out at 296. The weight of all the extra guns and ammo extracted a price on performance. Service ceiling in the XB-40 was limited to 29,400 feet, more than a mile and a half lower than that for a standard B-17F bomber variant.
The stage was set for bomber escort missions in 1943. A dozen YB-40s were sent to the 92nd Bomb Group at Alconbury, England. One additional YB-40 never made it to Alconbury, crash landing in Scotland on the way over. Between May and August 1943, the YB-40s flew combat missions with the 92nd as well as other Eighth Air Force bomb groups, to test their merit.
Several things manifested during the combat testing of the YB-40. Early on, the front gun of the twin-gun waist window mounts experienced ammunition feed issues and tail mounts had problems as well. The YB-40s stood down for a couple weeks while fixes were made in England.
When the bomber escorts returned to service alongside regular B-17Fs, the superiority of the YB-40s’ chin turrets in providing head-on protection quickly became apparent. The B-40s typically flew with the low squadron of a bombing formation since that was the grouping most likely to receive fighter attacks.
But while the YB-40s were fitted with additional armaments that protected the side and rear quarters, only the new chin turret gave added protection to frontal attacks. And that was where the attacks counted the most.
A statistical tally reported by Col. William Reid, commander of the 92nd Bomb Group, said the estimated increase in firing power of the YB-40 over a traditional B-17F was 20%, while the effectiveness of the bomber escort Fortresses against German fighters was only 10% better than a regular Fortress. The colonel added it was believed that the majority of this 10% increase in effectiveness “is in the Bendix chin turret.”
The YB-40s had additional liabilities in combat. Placement of the second top turret in the radio compartment blocked one avenue of escape, especially if ditching became necessary, and the dual waist guns obscured more of the waist openings for escape as well.
The YB-40s could keep up with the formation of loaded bombers inbound to the target, but once empty, the regular B-17s were faster on the exit unless the YB-40s flew with higher power settings, which aggravated gasoline consumption. The YB-40s ran at about 100 rpm faster than regular B-17s with 2 inches greater manifold pressure on trips home. And with that came a greater fuel burn, sometimes causing the returning YB-40s to seek the nearest landing field possible before running out of gas.
A damning tangent to this was the fact a heavy YB-40 could not maintain formation at all on three engines, and its chances of losing an engine on a mission were equal to that of the rest of the Fortresses in the formation.
AAF evaluators quickly rethought the wisdom of sending a crew and a converted heavy bomber like the YB-40 into harm’s way when the bomber no longer contributed to bombs on target, and its very configuration posed hazards to the crew.
The verdict was succinct: The YB-40 armed escort would not enter into mass production, but its revolutionary chin turret would, on late-delivery B-17Fs and especially on the B-17G model of the Flying Fortress.
Some of the YB-40s became trainers with the second dorsal turret removed. Ever-longer-ranging fighters became the answer to bomber protection from Luftwaffe fighters.
Yb-40 was a great escorte aircraft and if you want to write a new book I could prove this. I could show that this and 9 other aircrafts and 6 armored vehicles could have won the war in 2 yrs and new tactics and strategies could have won the war in one year. Thanks for your time. Need book cash deal only.