acoustically transparent epoxy, nanocomposites for underwater sonar windows J. Adv. Mater. 41  (2009) 5-17. 1 Carbon nanotube reinforced acoustically transparent epoxy nanocomposites for underwater sonar windows Wei Chen, Shankar Rajaram, Shad Thomas, Steven R. Nutt 1. Materials Science and Chemical Engineering, University of Southern CaliforniaVHE406, 3651 Watt Way, Los Angeles, CA, USA, 90089 2. ATS Consulting, 801 South Grand Street, Suite 575, Los Angeles, CA, USA, 90017 Abstract: Oxidized multiwalled carbon nanotubes (o-MWCNTs) were incorporated into filled epoxy blends to develop an acoustically transparent structural nanocomposites for sonar windows. The longitudinal wave speed, density, flexural mechanical properties, loss factor, and insertion loss were characterized for different compositions. The addition of 0.05wt% o-MWCNTs increased the composite flexural modulus and strength by 370% and 90% respectively with no change in the longitudinal acoustic wave speed. Analytical predictions also indicated that higher shear loss factor provided by carbon nanotubes ameliorated shear resonance at oblique insertion angles. Carbon nanotube additions afford the ability to increase mechanical properties and acoustic transparency, both of which are critical for underwater sonar windows.