The high noise levels being experienced in some military fast jet aircraft and helicopters generally result in a reduction in the intelligibility of speech communications. A study has been conducted to assess the effect of reducing noise levels at the ear, by the use of current Active Noise Reduction (ANR) systems, on speech intelligibility in aircraft noise environments. The results of this study indicate that ANR would improve speech intelligibility in both types of aircraft. The assessment has been conducted using Diagnostic Rhyme Test (DRT) and Articulation Index (AI) techniques. The study has also allowed the correlation between DRT and AI test results to be investigated. A more detailed account of the work reported in this paper is provided at [1].