The AN/PSG-2 Digital Message Device is a portable data-entry terminal used by artillery

Artillery

Originally applied to any group of infantry primarily armed with projectile weapons, artillery has over time become limited in meaning to refer only to those engines of war that operate by projection of munitions far beyond the range of effect of personal weapons...

 forward observers to communicate with artillery batteries to request and control artillery fire missions. DMDs were first fielded as part of the TACFIRE artillery fire control system.

The original DMD allowed the user to conduct fire missions, develop fire plans, and send/receive freeform text messages. An enhanced version, the FIST (FIre Support Team) DMD, allowed a FIST Chief (usually an Artillery Lieutenant

Lieutenant

A lieutenant is a junior commissioned officer in many nations' armed forces. Typically, the rank of lieutenant in naval usage, while still a junior officer rank, is senior to the army rank...

) to monitor the transmissions of his forward observers.

The accompanying illustration is from the Windows version of the MiniTSFO

MiniTSFO

The Mini TSFO was the first artillery call-for-fire simulation designed for a personal computer. It was started in 1985 as an outgrowth of a Field Artillery Officer Advanced Course battlefield research project at the U.S. Army Field Artillery School to develop a concept for incorporating PCs...

, a PC

Personal computer

A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...

-based call for fire simulator developed in the late 1980s.