This report presents designs for a component of the input-output system at every MALLARD terminal concerned with written messages. The Message Composition Applique MCA serves as a storage buffer between one or more teletypewriters and the high-speed 2400 baud MALLARD line. The MCA is essentially a small, special-purpose digital computer designed for use by technically unskilled personnel in a forward area environment. The operating procedure is communications-orientated and ensures that messages are prepared in a form suitable for transmission through an automatically switched communications system. The procedure allows editing, correction and verification of a stored message, and automatic insertion of pre-recorded data. Received messages are printed out in order of precedence times of arrival determine printout order within a precedence level. Two levels of message precedence are pre-emptive. The transmission or reception of a message is completely automatic and typically takes a few seconds.