B-17 Bomber Flying Fortress – The Queen Of The Skies Bombtypes and Bombsight

Bombtypes

General Purpose/High Explosive Bombs
The standard bombs used by the 8th Bomber Command from September 1942 were the five General Purpose types: the M30 100lb, M31 300lb, M43 500lb, M44 1000lb and M34 2000lb. Generally, 500lb, 1000lb, and 2000lb bombs were carried for industiral targets anf the other for airfields. The 8th Air Force used 1000lb and 2000lb bombs for attacks on sumarine pens but these had little effect on the vast concrete fortifications that sheltered the U-boats most of the damage was done to the surronding port area.

The General Purpose (GP) bombs used in the early missions were fitted with quarter second delay tail fuses with an extra tenth of a second fuse in the nose. In a report, in December 1942, after the raid on Lille, it was calculated that 30% of the bombs dropped had failed to explode because the arming mechanisms had frozen up after being exposed the damp conditions on the airfields overnight. Standard Operating Procedure was soon challanged so that fuses were installed just before take off. Eventually, to avoid accidents in landing, fuses were to be insered only when the bombs were securely fixed into the aircraft.

In 1943, a new set of GP bombs were produced: the M57 250lb, M64 500lb, M65 1000lb and M66 2000lb. These accounted for most of the bombs dropped in the final year of the war. In January 1945, experts recommended 250lb GP bombs to be used against synthetic oil plants, ammunition dumps and oil storage factilities. the 100lb bomb was recommended for attacking railway yards and runways.

Incendiary Bombs
Originally, the only incendiary bombs were available were the British 250lb and 500lb models filled with a rubber/gasoline mix, but in November 1942 the American M50A1 41lb magnesium bomb was added to the arsenal. It was packed in 100lb clusters which had a tendency to open prematurely, diperse too widely and cause damage to other planes in the formation. In Jnuary 1944, the US 8th Air Force used the 500lb M17 cluster which had better ballistics and a primecord release that could be set to give correct disbursement. This became the most favored and effectice incendiary bomb among the bomber Groups.

High explosive and incendiary bombs fell through the air in varing trajectories and thus an accurate attack with a mixed load was very difficult to aim. For this reason, timelag tables were esed to indicate the release interval times of the different types of bomb. Eventually, factors such as wind speed and altitude were also taken into account.

Napalm Bombs
In the latter half ob 1944 a refined petroleum jelly called Napalm became available. Known as Class-C Fire Bombs and with a capacity of 108 US gallons, these bombs were only used in few missions. A B-17 carried four such bombs with tiny igniter units fitted to each tank.

Fragmentation Bombs
Used as anti-personnel bombs during ground force support attacks, these 20lb M41’s were fitted in 120lb and 500lb clusters. They were very lighty bombs and the B-17 Nordon bombsight had to be used with a special computation table to provide the maximum trail angle (distance between plane and point of impact).

Poison Gas Bombs
Poisen gas bombs were kept in stock as a deterrent throughout the war by the US 8th Air Force. they consisted of two types, both made in Britain; the 400lb “Flying Cow” mustard gas bomb and the 500lb phsogene bomb.

VB-1 AZON-Bomb
A basic 1000lb bomb but with a special tail attachment which allowed it to be steered over a distance of 200 feet to eighter side of the point of impact from a heigh of 20,000 feet. They were controlled by the dropping aircraft using an AN/ARW-9 transmitter. The bomb could only be attached to a B-24 on a 2000lb bomb shackle.

GB-1 Glide Bomb
This was made from a M34-2000lb bomb fixed to a 12 foot span glider unit and attched to a B-17 underwing shackle. Two Glide bombs could be carried per plane. essentially free fall, the bomb had a stabilizing device that allowed control of direction. The bomb proved to be unreliable on the only occasion it was used on Cologne in April 1944.

GB-4
A radio controlled bomb with a TV camera fitted in the nose section that transmitted a TV signal over a range of 15 miles. It was only ever used on one plane, a B-17, on a single combat sortie.

Disney Rocket Bomb
This 4500lb bomb was designed for penetrating the thick concrete U-boat shelters. It was free-fall until a rocket motor fired at 5,000 feet, pushing the missile to speeds of 2,400 feet per second upon impact. It could penetrate 20 feet in solid concrete before explosion and was first used by 92nd Bomb Group on 14th March 1945.

Bombsight

The Vector Sight
The bombardier had to set the aircraft speed and altitude, determine wind speed, direction and the bomb load ballistic data. He would look at a sighting cross made of thin pieces of wire, or lines of light on a screen, which showed where the bombs would hit if dropped at that particular moment. The Vector Sight needed a long horizontal approach and was not suited to a monoplane which tended so shift sideways as it banked for turns. In 1942, the RAF produced the Mark 4 which was gyro-stabilized and allowd the aircraft to make banked turns on a bomb run. It worked by passing the data to a complex analouge computer which corrected the sight to take account of any course deviantion.

Tachometric Sight
During a bomb run a bombardier looked through a sighting telescope at the target. The sight was adjusted by a variable speed electric motor. The bombardier input bomb load and altutude data, then set the telescope sight over the target. The base of the sight was gyrostabilized and, by keeping the telescope on the target, aircraft movement information was fed into the sighting computer. The computer produced course correction signals that were channeled to the pilot’s panel. When the bomber was close to the target, the sight telescope was almost vertical and the computer calculated when the release angel had been reached. Then a series of electric contacts were closed and the bombs dropped automaticlly.

The US version of the Tachometric sight was called “NORDEN”¹. Later models of the “Norden” channeled data directly into the auto pilot and effectively, the bomb aimer could “fly” the plane by fine adjustment of the sighting telescope. The main disadvantage of this sight was that it needed at least 20 seconds of nondeviational flight. It also lost accuracy if fire and smoke obsured the target.

¹ Also called “Norden”