radio waves travel much faster than sound waves. Radio waves travel about 330 yards in a millionth of a second. Therefore, the times involved in radar ranging are much shorter than for sound ranging. APPLICATIONS OF RADAR Radar was originally devised as an instrument to detect approaching ships or aircraft. Practice and experience in reading the scope soon showed that radar could do much more. By plotting successive positions of enemy ships and aircraft, you could determine their course and speed. Further experience made it possible to determine whether the target was a battleship, destroyer, aircraft, or a group of targets. Also, an aircraft's altitude could be determined. Use in Tactical Air Control Both airborne and shipboard radar is a major link in an operational system. It directs fighter aircraft to a favorable position for intercepting enemy aircraft. The air control officer can determine the number of fighters so they can successfully attack and destroy the enemy. Airborne early warning (AEW) aircraft, equipped with high-powered radars, are used in tactical air control. These aircraft extend the range of air control radar by operating in areas outside the range of the shipboard or land-based radar. The Aviation Electronics Technician (AT) rating maintains AEW equipment. Use in Fire Control The highly directional characteristics of radar make it suited for directing fire control systems. Focusing the radar energy into a narrow beam enables it to display target position with a high degree of accuracy. At the same time, it also displays target range. The primary purpose of fire control radar is to determine the correct position and attitude the aircraft should be in to hit the specified target. Radar, in its early stages of development, was useful as an aid to the human eye under poor visibility conditions. It also provided a more accurate and faster means of range measurement. Presently, it provides a faster and more accurate method of directing fire control than is humanly possible. This feature is extremely important considering the high speeds of today's aircraft and missiles. The time available to launch an intercept weapon effectively is measured in fractions of a second. IDENTIFICATION FRIEND OR FOE (IFF) The problem of distinguishing friend from foe in warfare has increased because of the increased speed of aircraft and ships. Radar can detect both sea and air targets at long range. However, it displays both friend and enemy similarly on the scope. It is not practical to wait until the target has been visually identified to begin preparing for battle. A method other than visual recognition must be used for early identification of the target. IFF is an electronic system that allows a friendly craft to identify itself automatically before approaching near enough to threaten the security of other naval units. A transponder in the friendly aircraft receives a radio-wave challenge (interrogation). The transponder transmits a response to a proper challenge, as shown in figure 7-24. Upon receiving the proper challenge, the transponder automatically transmits a coded reply, which tells the challenger that a friend has been challenged. The transponder stays in a standby condition and transmits only when the proper challenge is received. The challenger's receiver accepts the reply of the challenged target and presents the replies on an indicator. All operational aircraft and ships of the armed forces carry transponders to give their identity when challenged. For operations involving only friendly 7-18 MODE 1 REPLY UNFRIENDLY OR UNEQUIPPED CRAFT EMERGENCY REPLY MODE 1, 2 OR 3/A 1/P REPLY MODE 1, 2 OR 3/A MODE 3/A REPLY RADAR ECHO MODE 2 REPLY ANF0724 Figure 7-24.—Typical surface radar PPI composite display showing several IFF responses.