Convergence is the angular correction in yaw applied to a gun's aim so that its fire falls on the point of aim provided by a remote gunsight. It is a component of the design of a mature Director Firing system.
For any gun removed by a given base length along the centerline from the director on own ship, when firing on a target on a given relative bearing, the convergence correction will be:
convergenceAngle = arctan(sin(relativeBearing) * baseLength / range)
The British director firing system calculated and applied convergence corrections in the Training Receivers. The design was fairly elegant, but each training receiver could only be made to work relative to one director[Inference], and the operator had to provide the additional input of Gun Range. The instrument received its relative bearing input directly from the turret's orientation, and its base length from the director was reflected by the shape of spiral cams within the receiver.
- Dip, the analogous correction in pitch (elevation)
- The Director Firing Handbook. pp. 11-2.
- Admiralty, Gunnery Branch (1917). The Director Firing Handbook. O.U. 6125 (late C.B. 1259). Copy No. 322 at The National Archives. ADM 186/227.