Call Signs The following call signs are authorized for use in calling and answering: visual, international, tactical, task organization, collective, and indefinite. Address groups may be used as call signs by Coast Guard and Navy commands (except in non-military communications.) Call signs and address groups in message headings will ordinarily be arranged in alphabetical order in the form in which they are transmitted, whether plain, encrypted, or mixed. For this purpose, / (slant sign) and figures 0 through 9 will be considered the twenty-seventh through thirty-seventh letters of the alphabet. Care must be taken to avoid separating groups of related call signs or conjunctive address groups, which are interdependent. The different methods of visual signaling require variations in procedure for calling and answering. The necessary instruction for each method is prescribed throughout this chapter. FLASHING LIGHT PROCEDURES LEARNING OBJECTIVES: Explain the procedure for calling, answering, relaying, verifying, repeating, correcting, and receipting using directional and non-directional flashing light. Identify procedures for communicating with aircraft, with daylight signaling lantern (DSL), and infrared. The two forms of flashing light used are directional and non-directional. Directional procedure is always employed when using a directional light. It is also employed when using a non-directional light when the call is that of a single station. Non-directional procedure is one station transmitting to a number of other stations simultaneously by means of a light showing over a wide area. See appendix II for tips for sending and receiving flashing light. USE OF SIGNAL LIGHTS In wartime, the greatest care is to be taken when signaling at night. Flashing light is to be used only when necessary and a minimum of light employed except when making recognition signals. Then, a light of sufficient brilliancy must be used to ensure its being immediately seen. You must, however, always remember that in heavy weather small ships have trouble reading dim lights. The background must always be considered, and care should be taken not to use a signaling light close to or in line with navigation lights. No upper-deck lighting should be visible on or in the vicinity of the signal deck. The use of signal lights at dusk and dawn must be avoided whenever possible. If, however, their use is unavoidable, you must pay constant attention to the brilliancy of their light. At night, a constant watch is to be kept on the ship of the OTC by all other ships. It may be found, after communication has been established, that the brilliancy of the light can still be further reduced. It is absolutely essential when using any type of directional light to keep it trained accurately throughout the transmission of the message. At all times, ships are to inform other ships signaling to them when their lights are observed to be brighter than necessary, by use of the prosign D. Frequently test sight arrangements of lights for alignment. To prevent masthead and yardarm signaling lights from being accidently lighted, the switch in the power supply line should be kept open until use of the light is actually required. DIRECTIONAL PROCEDURE The transmitting station waits for the receiving station to make a flash for each word, prosign, coded group, or operating signal. Should the receiving station fail to flash for the group, it will be repeated by the transmitting station until a flash is received from the receiving station. An exception to this rule is that a flash is not necessary to the prosign K when there is an immediate response to K. A flash should be made to K in the message ending when there will be a delay while checking the message to ensure its completeness. NON-DIRECTIONAL PROCEDURE This procedure permits one station to transmit to a number of other stations simultaneously by means of a light showing over a wide area. It is seldom used at night in wartime because of the danger of enemy interception. It may be used by day or night in circumstances where the risk is negligible. The procedure prescribed for the non-directional flashing 4-4