(one or two degree) beam width. Atmospheric conditions, such as moisture lapse, temperature inversion, and dust particles affect radar performance as well. Moisture lapse and temperature inversion often cause ducting, in which RF energy is bent as it passes through hot and cold layers. This can either extend or shorten the radar horizon, depending on which way the RF is bent. Dust particles, as well as water droplets, cause attenuation of the RF energy, resulting in a loss of effective range. In both cases, a lower pulse repetition frequency makes the radar less susceptible to atmospheric conditions. Countermeasures Most fire-control radars have unique characteristics, such as radio frequency, pulse duration, pulse frequency and power. These can assist in identifying the radar, and therefore the weapon system it is controlling. This can provide valuable tactical information, like the maximum range of the weapon, or flaws that can be exploited, to combatants that are listening for these signs. During the Cold War Soviet fire control radars were often named and NATO pilots would be able to identify the threats present by the radar signals they received. Surface based One of the first successful fire-control radars, the SCR-584, was used effectively and extensively by the Allies during World War II for anti-aircraft gun laying. Since World War II, the U.S. Army has used radar for directing anti-aircraft missiles including the MIM-23 Hawk, the Nike series and currently the MIM-104 Patriot. Ship based Examples of fire-control radars currently in use by the United States Navy: Mk 95 — Continuous Wave Illuminator (NATO Sea sparrow Surface Missile System) Mk 92 — Combined Antenna System (Mk 75 Gun, formerly SM-1 missiles) AN/SPG-62 — Continuous Wave Illuminator (AEGIS) AN/SPQ-9B — Pulse Doppler (Mk 45 lightweight gun) Aircraft based After World War II, airborne fire control radars have evolved from the simpler gun and rocket laying AN/APG-36 system used in the F-86D to the active electronically scanned array-based AN/APG-81 of the F-35. See also Radar configurations and types List of radars List of military electronics of the United States Ship gun fire-control system References US Navy, FIRE CONTROLMAN, VOLUME 02—FIRE CONTROL RADAR FUNDAMENTALS (Revised) External links AN/APG Fire Control Systems at GlobalSecurity.org Military radars