A two-year Army study effort related to a large procurement of VHFFM and HFSSB radios for Army helicopters is described. The communication problem, requirements and solutions for helicopters flying nap-of-the-earth NOE in the modern battlefield are given. A model for predictions of communication ranges in irregular terrain terrain, noise environment and radio system parameters as variables was developed. Model inputs are median basic transmission loss from Longley-Rice, man-made, atmospheric, and galactic noise CCIR Reports 258 and 322, candidate radio system parameters Transmitter ERP and required SNR at receiver, and the standard deviations of these parameters. The model output is the probability of successful communication, ps, at a given range in irregular terrain. The model was used in the European SCORES scenario to predict communication and mission effectiveness in the Fulda region for candidate radio systems. Limited model validation data are given. Quantitative test results for the TCATA FM-320 NOE communication test are given and discussed. These tests compared the ANARC-114 Baseline radio with other radio candidates - 40-W VHF, Retransmission, and HFSSB. In addition, quantitative results are given for VHFFM, HFSSB, and satellite NOE systems tests. Technical appendices contain information on OH-58 VHF and HF helicopter antenna gain dBi, FSK data transmission, speech processing, and HF and VHF field strength measurements.