David Porter on military history’s doomed inventions
When the USAAF’s Eighth Air Force arrived in Britain in mid-1942, it was confident that unescorted formations of B-17 Flying Fortresses could make precision daylight bombing raids without suffering serious losses.
The theory was that the combined defensive armament of large bomber formations would fend off fighter attacks, while the Norden bomb-sight would allow accurate bombing from altitudes at which flak (AA fire) was ineffective.
The first short-range missions in the autumn of 1942 seemed to vindicate the theory, but these were heavily escorted by RAF fighters. As deeper-penetration raids began in the winter of 1942/1943, Allied fighters lacked the range to protect the bombers all the way to their targets.
The weather made matters worse, as cloud cover frequently forced the bombers to attack at relatively low altitude, where flak was more accurate. These factors caused losses to mount alarmingly – reaching an average of almost 10% per raid in early 1943.
The idea of a heavily armed ‘gunship’ version of the B-17 to escort bombers beyond fighter range had been proposed several months earlier. Work on a prototype, based on an early production B-17F, began in September 1942.
A second dorsal turret was installed in the former radio compartment, just behind the bomb bay. The single 0.5-inch Browning machine-gun in each waist position was replaced by twin guns, and the nose was modified to mount a remote control Bendix ‘chin’ turret with twin 0.5-inch Brownings.
A 16-gun dinosaur
This gave the aircraft a total of 16 guns, each of which fired 13 rounds per second. To cope with this, the bomb bay was converted to hold almost 11,000 rounds of ammunition.
Unconfirmed reports indicate that a few aircraft were experimentally fitted with anything up to 30 assorted guns, although the weight of such an arsenal and its ammunition would have drastically worsened speed and rate of climb, which were poor enough already.
The new type, designated YB-40, seemed promising, but the extra armament and ammunition, coupled with additional armour protection for the new gun positions, dramatically increased weight, which was 4,000lbs greater than that of a standard B-17F.
Drag was also a problem, with the YB-40 taking 48 minutes to struggle up to 20,000 feet, whereas a B-17F could reach the same altitude in 25 minutes.
Despite this, a total of 12 YB-40s were sent to the 327th Bombardment Squadron for combat trials in mid-1943. On 29 May, seven aircraft made the type’s operational debut, during which they struggled to keep up with the B-17s on the outward flight. On the return journey, the situation was even worse, as, aft er dropping their bombs, the far-lighter B-17s completely outpaced their escorts.
It soon became clear that this was an insoluble problem. YB-40s took part in only 14 raids before they were withdrawn from combat at the end of July 1943.
Although the type was totally ineffective in its intended role, the ‘chin’ turret was found to be so useful in fending off head-on attacks that it was fitted as standard to the 8,680 B-17Gs completed between August 1943 and the end of the war.
This article was published in the January 2020 issue of Military History Matters. To find out more about subscribing to the magazine, click here.