The basic principle of any bombing mission was to deliver the bombs accurately on the target. To navigate through clouds or to evade and counter the enemy’s defenses was an achievement in itself, yet everything depended upon the bombardier’s ability to hit his target. The bombardier’s main tool was the Norden bombsight, a top secret piece of equipment the Allies guarded throughout the war. On a mission, the bombardier’s real job began at the IP. This was the point at which the bombing run on the target began; from this point on, the bombardier would fly the airplane through the bombsight linked to the autopilot.
The plane would have to be flown straight and level to the release point through flak and fighter attacks. Few, if any, bombers equalled the B-17 in visibility afforded to the bombardier. Sitting behind the bombsight in the plexiglas nose gave him an unrestricted view for his mission. The Norden simplified the bombardier’s job considerably by taking into account factors of altitude, airspeed, ground speed and drift to automatically calculate the bomb release point.
The optical sighting mechanism of the bombsight was a small telescope. The bombardier would first locate the target by looking over the instrument and through the plexiglas nose. Once the target was located he would try to line it up in the telescope, often requiring several head up glances to find the target again. There were two cross hairs on the telescope, one to show drift left or right of the target, the other to show rate of closure. When the two indicators met the bombs would automatically release.
Originally the bombardier had a .30 caliber machine gun in the plexiglas nose but this was soon changed to a more effective .50 caliber. In late 1943, a powered chin turret was added to help combat frontal attacks and became standard equipment on the B-17G.