The first instrument was used to calculate the deflection due to own ship's movement (which is not used as a component in torpedo deflection), the second to compute the rate of change of bearing, and the third to calculate the torpedo deflection.
An Anschutz gyro compass receiver was situated below a telescope geared to a pointer. In the image, spindle "a" is cut below the worm-wheel. A second spindle inside carries the pointer. When the telescope carrier is turned, the motion is carried through the inner spindle, with the amount of motion being read off the card. The outer spindle carries the gyro compass motor's movement to the inner card.
The lower end of the telescope carrier has a bar, fixed to be parallel to own ship's keel and graduated to in knots. A sliding pointer carried along this bar is set to own speed. This bar sweeps over a sector card of about 9 inches radius and 120 degrees arc which is fixed rigidly to the frame of the gyro compass and is marked with a deflection scale.
When the telescope is pointed at the target, the pointer on the own speed arm will indicate the component of Speed Across which is attributable to own ship's motion. This will be the amount we want to subtract from the speed across to obtain the final figure of torpedo director deflection.
This device was a simple circular calculating disc used to assist in a timed period of use of the Bearing Instrument.
A moving card marked exactly as the inner gyro compass card of the Bearing Instrument was mounted on a sheet of brass carrying a fixed index pointer. Another pointer was pivoted at the center of the disc so it could spin freely.
Around the movable card were 2 circular scales, the inner one being for an interval of 45 seconds, and the outer one being for 30 seconds. The device, then, is used during a given interval of set duration.
At the beginning of the 30- or 45-second trial, the rotating card it spun so that its reading relative to the fixed pointer matches that shown on the Bearing Instrument. When the trial has elapsed, the moveable pointer is positioned to the present reading of the inner gyro card of the Bearing Instrument. The reading at the appropriate fixed, outer scale for the duration of the trial then indicates the bearing rate in degrees per minute.
The third device has a large drum and a smaller one with a circular end face.
The large drum's face is etched with bearing rate vs range lines, and the small one with own ship's deflection on its circumference and enemy deflection on its circular face. A knob moves a pointer along the face of the larger drum to enter the range to the target. The large drum is then rotated so that the line representing the present bearing rate touches the range pointer. As the large drum is rotated, a moving pointer revolves about the circular face of the smaller drum. The smaller drum is spun until own ship's deflection as read off its circumference matches the fixed pointer, and the proper torpedo deflection is then read off the circular face of the smaller drum, as indicated by the moving pointer.
- Annual Report of the Torpedo School, 1914, p. 33-34.
- Annual Report of the Torpedo School, 1914, Plate 12
- Annual Report of the Torpedo School, 1914, Plate 13
- Annual Report of the Torpedo School, 1914, Plate 14
- Annual Report of the Torpedo School, 1914, Plate 15
- Annual Report of the Torpedo School, 1914, Plate 16
- Annual Report of the Torpedo School, 1915. p. 60.
- H.M.S. Vernon. Annual Report of the Torpedo School, 1914. Copy 5 at The National Archives. ADM 189/34.
- H.M.S. Vernon. (Jan 1916) Annual Report of the Torpedo School, 1915. C.B. 1166. Copy 1025 at The National Archives. ADM 189/35.
- Admiralty, Gunnery Branch (1917). Handbook of Torpedo Control, 1916. C.B. 302. Copy No. 141 at The National Archives. ADM 186/381.