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The YB-40 was developed to test the bomber escort concept. Early in World War II, before
long range fighters like the P-51D became available, the Air Corps developed plans to
modify bombers with additional defensive armament.
These aircraft would accompany regular bomber formations and provide protection from
attacking fighters. Unfortunately, the modified escort bombers were not maneuverable
enough to protect large formations.
They were also excessively tail heavy and overweight. A standard B-17F formation returning
from a mission (after bomb release) outpaced the escort bombers.
The YB-40 participated in only a few operational missions in mid-1943 before being
withdrawn from service.
The prototype XB-40 was modified by Lockheed Vega (Project V-139) by converting the second
production B-17F-1-BO (S/N 41-24341). Defensive armament consisted of fourteen .50-cal.
machine guns in seven gun positions: chin turret, two dorsal turrets, ball turret, two
waist positions and the tail.
The first flight of the XB-40 was on 10 November 1942. Twenty service test aircraft were
ordered (Vega Project V-140) as YB-40 along with four crew trainers designated TB-40.
Because Vega had higher priority production projects, the YB-40/TB-40 assembly job was
transferred to Douglas.
In the spring of 1943, the 327th Bomb Squadron of the 92nd Bomb Group, RAF Alconbury was
assigned twelve YB-40s for operational combat tests. The first mission was flown on 29 May
1943 and after less than ten missions the aircraft were withdrawn from service. Most were
converted back to the standard B-17F configuration.
The chin turret installation pioneered on the B-40 series aircraft was soon adopted for
late model B-17Fs and became standard equipment on the B-17G.
TYPE
XB-40
YB-40
TB-40
Number Built/Converted
1 (cv)
20 (cv)
4 (cv)
Remarks
B-17F converted to bomber escort
Service test version
YB-40 crew training aircraft
Notes:
Serial numbers: XB-40 (B-17F-1-BO): 41-24341;
YB-40 (B-17F-VE): 42-5732 to 42-5744, 42-5871, 42-5920, 42-5921, 42-5923 to 42-5925,
42-5927;
TB-40 (B-17F-VE): 42-5833, 42-5834, 42-5872, 42-5926
First flight of the XB-40 was 10 November 1942
SPECIFICATIONS
Span: 103 ft. 9 in.
Length: 74 ft. 9 in.
Height: 19 ft. 1 in.
Weight: 63,500 lbs. (max. gross weight)
Armament: Fourteen .50-cal. machine guns standard, various numbers and types of machine
guns and cannon were also tested.
Engines: Four Wright R-1820-65 engines of 1,200 hp. each.
Crew: 9
PERFORMANCE
Maximum speed: 292 mph. at 25,000 ft.
Cruising speed: 196 mph
Range: 2,260 miles
Service Ceiling: 29,200 ft.
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