1. An adapter for mounting a target sight device to a handheld mortar, the mortar having a launch tube with a center axis extending the length of the tube, and a base plate for supporting the mortar during use, the adapter comprising: a mounting structure for mounting the adaptor to the launch tube of the mortar in a manner whereby the mounting structure is reliably aligned with said center axis of the tube; a rail structure for mounting a target sight device, wherein said rail structure is associated with a pivot assembly and said rail structure pivots relative to the mounting structure to accurately sight a target; a curved bubble level mounted in a housing with a graduated scale indicative of the angle of tilt from vertical of the center axis of the mortar tube; a tilt sensor whereby the tilt sensor is configured to be aligned with the central axis of the mortar tube and determines the angle of inclination of the central axis relative to the ground; and a data processing module, the data processing module comprised of a microcontroller having a memory and capable of executing machine readable instructions, a user interface whereby a user can selectively input data related to ballistic profile of a projectile, and a display for presentation of information to said user.