1. After making IP turn, course is set for Aiming Point. Plan Position Indicator is set for Zoom and Sector Scan to enlarge and keep the critical area in view.

2. Range Circle is set for the precomputed slant range from aircraft to Aiming Point. When the circle reaches the Aiming Point the aircraft is at a 70-degree sighting angle to target

3. The bomb bay doors are open and the Norden Bombsight is running. Rather than visually sighting through the eyepiece, the bombardier’s attention is focused on the rate knob which he will set at 70 degrees when the radar officer says “70 Mark”.

4. A new slant range circle is set at a precomputed slant range, which corresponds to a 64 degree sighting angle to target. Radar says “Coming up on 64”. At “64 Mark” bombardier adjusts the rate knob to the 64-degree point. The rate may be too fast or too slow.

5. A third mark is made at 58 degrees. At this point a slight adjustment is made if necessary. The Norden Bombsight, which has been programmed with inflight data and aimed by Radar, takes over and releases the bombs at the proper instant.

6. The Radar screen at the Navigator’s position had photographed the bomb run and the belly camera on the fuselage had photographed the impact of the bombs below. At “Bombs Away” the screen is reset to a 50 Nautical Mile range and control is returned to Navigator and Airplane Commander. Evasive action was most often necessary at this point and Radar assisted in determining our position at its conclusion.

7. During the bomb run the course was controlled by the Radar Officer by calling a correction to the pilot or making the correction with the Correction Knob at his position.

8. The elapsed time from “70 Mark” to “Bombs Away” averaged 90 seconds to two minutes depending on altitude.

Rather Primitive Slant Range Table produced at Group Operations level. The values are in nautical miles for creation of the rangle circle. The table was used for direct bombing, aircraft to target only. Offset bombing, using aiming point ahead of the target, required additional calculations

Spacing

Bombs could be salvoed or programmed to drop at intervals, creating a train of hits. The intervalometer on the bombsight regulated these intervals. The setting for pathfinders was 100 feet which produced a trail of about 1000 feet, a very visible target for the attacking force following. The setting for the attacking force following was 50 feet, concentrating more bombs in a smaller area. The fires started by these hits would spread, meet and increase in intensity. The individual fires would merge into one huge firestorm, which would merge into adjacent firestorms started by other attacking forces. With air rising from the intense heat, a low-pressure weather system was generated, causing violent updrafts and gale force winds, contributing to the spread of the flames.

Using this method, a total of 56.3 square miles of Tokyo was destroyed in six raids. The greatest destruction in a single raid was 15.8 square miles on March 9, the initial raid of the series, and another 15.8 square miles on May 25, the last raid of the series. Leaving the southern coast of Japan the fires were visible for over 100 miles.

Another version of the Slant Range Table.  The 70, 64 and 58 degree values were more widely used.