For the past 12 yr, a coordinated triservice effort has been under way in the U.S. Department of Defense to provide an atmospheric effects assessment capability for existing and planned electro-optical (EO) systems. This exploratory development effort by the U.S. Navy is reviewed. An initial marine aerosol model, the Navy Aerosol Model (NAM), which transitioned into LOWTRAN 6, and a more comprehensive model, the Navy Oceanic Vertical Aerosol Model (NOVAM), are discussed. In addition to marine aerosols and their extinction properties, accurate knowledge of marine background radiances and the effects of the intervening atmosphere are needed. Because in situ measurements of relevant environmental parameters are essential for real-time EO systems performance assessment and direct measurement of slant path extinction is most desirable, light detection and ranging (LIDAR) techniques are being developed. No technique, however, has yet emerged that is ready for shipboard implementation. A shipboard real-time performance assessment system, PREOS (performance and range for EO systems), has been developed and incorporated into the Navy's Tactical Environmental Support System (TESS), and improved target and background models are under development and will be incorporated into TESS when tested and validated. A reliable assessment capability can be used to develop tactical decision aids (TDAs), which permit optimum selection or combination of sensors and estimation of a ship's vulnerability against hostile systems.