Boeing YB-40 Flying Fortress Escort Bomber

The Boeing YB-40 Escort Bomber or “Bomber-Fighter” was a B-17 with additional defensive armament, armor, and ammunition built in an attempt to provide defense for B-17 formations over Europe. This is the prototype XB-40, converted from the second production B-17F-1-BO serial number 41-24341 by Lockheed-Vega. Note the second dorsal turret mounted in the radio room and how the upper fairing extends to the turret.

Another photograph of the XB-40 prototype 41-24341. By this time the dorsal fairing has been abruptly truncated which increased drag but improved the fields of fire for the second turret. This would become the standard for the subsequent YB-40 series. If you look closely you can see some artwork on the fuselage side ….

… and here is a close-up. Mickey Mouse was a popular subject for aircraft artwork, and not just among American aircrews. Notice how the bars and red surround added to the national insignia have been applied over the artwork.

A total of twenty-five B-17F were modified to YB-40 or TB-40 (gunnery trainer) standard. Here is a photograph of 42-5732 through 42-5745 which were delivered to the modification center at Tulsa in October and November of 1942 receiving their modifications. The work to install the powered turret in the radio compartment is underway.

A well-known photograph showing the increased firepower of the YB-40 with eight of the fourteen .50 caliber machine guns visible. Several different armament configurations were proposed, including 40 mm or 20 mm cannon, and reportedly one with a total of thirty .50 caliber guns.

A nice external view of the port waist gun position showing the twin .50 calibers mounted there. Note the wind deflector forward of the opening and that the twin guns are mounted at the center of the window, not more forward as was standard for the single-gun installation.

A view from inside the YB-40 looking forward, showing the improved dual waist gun installation. The YB-40 introduced the staggered waist gun layout to the Flying Fortress design, this picture shows a modification to improve the ammunition feed to the guns. Note the large quantity of ammunition carried for these guns and the effort to shift the weight forward.

A major innovation was the installation a Bendix remote turret under the Bombardier’s position to improve forward firepower. Both German and Japanese pilots quickly discovered the relative weakness of frontal firepower of the Flying Fortress and concentrated their attacks from the nose whenever possible. This installation proved a success prompting Douglass to install Bendix chin turrets on the final eighty-six B-17Fs they produced, the Bendix turrets became standard at all three manufacturers with the B-17G model. This YB-40 does not yet carry cheek guns for the Navigator, although these would be added later.

YB40_08_42-5743_Woolaroc_42-5741_Chicago_ 92BG
Twelve YB-40s were assigned to the 92nd Bomb Group / 327th Bomb Squadron for combat trials where they flew missions from May through July 1943. This is 42-5743 “Woolaroc” and 42-5741 “Chicago” which operated from RAF Alconbury. The port cheek guns have been fitted on both these aircraft.

YB40_09_42-5736 -Tampa Tornado 92nd BG 327th BS
42-5736 “Tampa Tornado” at RAF Kimbolton during an open house for local schoolchildren. The subdued national insignia is apparent, Neutral Gray was substituted for the more usual Insignia White.

The Tampa Tornado again with two sisterships at Alconbury. The YB-40 experiment was not deemed a success. While firepower was improved it was still not sufficient to deter the Jagdwaffe. The YB-40 contributed nothing to the total bombs on target, and the weight of the additional guns and ammunition made it difficult for the YB-40s to keep up with a B-17 formation, especially after they had released their bomb loads.

The YB-40s were withdrawn from the European Theater and redesignated as TB-40s where they served Stateside in the gunnery training role. Here is 42-5925 along with four Bell P-63 King Cobras on a training flight.

Here is 42-5741 Chicago again, likely at RFC Ontario at the end of her service life. Note the lack of armament and the large training “buzz number”. Upon her return to the States she was renamed “Guardian Angel”. All of the YB-40s were scrapped after the war, none survive today. In the final assessment the YB-40 program contributed improvements to the defensive armament of standard Flying Fortresses, primarily the staggered waist gun positions and the Bendix chin turret in the nose.

YB-40 missions log from Wikipedia:

29 May 1943 – attacked submarine pens and locks at Saint-Nazaire. Smaller strikes were made at Rennes naval depot and U-boat yards at La Pallice. In the attack, seven YB-40s were dispatched to Saint-Nazaire; they were unable to keep up with B-17s on their return from the target and modification of the waist and tail gun feeds and ammunition supplies was found to be needed. The YB-40s were sent to Technical Service Command at the Abbots Ripton 2nd Strategic Air Depot for modifications.

15 June 1943 – four YB-40s were dispatched from Alconbury in a raid on Le Mans after completion of additional modifications.

22 June 1943 – attack on the I.G. Farben Industrie Chemische Werke synthetic rubber plant at Hüls. The plant, representing a large percentage of the Germany’s synthetic rubber producing capacity, was severely damaged. In the raid, 11 YB-40s were dispatched; aircraft 42-5735 was lost, being first damaged by flak and later shot down by Uffz. Bernhard Kunze in a Focke-Wulf Fw 190A-2 of JG 1 over Pont, Germany. The 10 crew members survived and were taken prisoner.

25 June 1943 – attack on Blohm & Voss sub shops at Oldenburg. This was the secondary target, as the primary at Hamburg was obscured by clouds. In this raid, seven YB-40s were dispatched, of which two aborted. Two German aircraft were claimed as destroyed.

26 June 1943 – scheduled but aborted participation in attack on the Luftwaffe air depot at Villacoublay, France (primary target) and also the Luftwaffe airfield at Poissy, France. The five YB-40s assigned to the attack were unable to form up with the bombing squadron, and returned to base.

28 June 1943 – attack on the U-boat pens at Saint-Nazaire. In the raid, the only serviceable lock entrance to the pens was destroyed. In this attack, six YB-40s were dispatched, and one German aircraft was claimed as destroyed.

29 June 1943 – scheduled participation in attack on the Luftwaffe air depot at Villacoublay, but aircraft returned to Alconbury due to clouds obscuring the target. In the raid, two YB-40s dispatched, one aborted.

4 July 1943 – attacks on aircraft factories at Nantes and Le Mans, France. In these raids, two YB-40s were dispatched to Nantes and one to Le Mans.

10 July 1943 – attack on Caen/Carpiquet airfield. In this raid, five YB-40s were dispatched.

14 July 1943 – attacked Luftwaffe air depot at Villacoublay. In this raid, five YB-40s were dispatched.

17 July 1943 – YB-40s recalled from a raid on Hannover due to bad weather. In this raid, two YB-40s were dispatched.

24 July 1943 – YB-40s recalled from an attack on Bergen, Norway due to cloud cover. In this raid, one YB-40 was dispatched.

28 July 1943 – attack on the Fieseler aircraft factory at Kassel. In this raid, two YB-40s were dispatched.

29 July 1943 – attack on U-boat yards at Kiel. In this raid, two YB-40s were dispatched.

Altogether of the 59 aircraft dispatched, 48 sorties were credited. Five German fighter kills and two probables were claimed, and one YB-40 was lost, shot down on 22 June mission to Hüls, Germany. Tactics were revised on the final five missions by placing a pair of YB-40s in the lead element of the strike to protect the mission commander.

Serials from Freeman:

41-24341 XB-40 prototype


42-5733 Peoria Prowler

42-5734 Seymore Angel, later renamed Red Balloon, Old Ironsides

42-5735 Wango Wango, lost on Hüls raid 22JUN43

42-5736 Tampa Tornado

42-5737 Dakota Demon

42-5738 Boston Tea Party

42-5739 Lufkin Ruffian

42-5740 Monticello

42-5741 Chicago, later renamed Guardian Angel

42-5742 Plain Dealing Express

42-5743 Woolaroc

42-5744 Dollie Madison










42-5833 TB-40 crew trainer

42-5834 TB-40 crew trainer

42-5872 TB-40 crew trainer

B-17 “Dreamboat” conversion here: