In addition to megaphone, radio, and blinker messages, various visual signals are used in beach operations, as shown in NWP 22-3, appendix C. Visual Emergency Signals for Boats The following signals are visual emergencies: OSCAR flag—Man overboard Life jacket on perpendicular boat hook— Breakdown BRAVO flag—Fire/flooding ZULU flag—Loss of receive/transmit communications GRID REFERENCE SYSTEM LEARNING OBJECTIVES: Explain the purpose of the grid reference system. Identify procedures for using it. The amphibious grid reference system is used primarily to control waves moving in the lanes from the rendezvous area to and across the LOD and until they land on the assigned beach. The grid is an overlay composed of a series of boat lanes (LOD to beach), one for each scheduled wave. Each boat lane is marked with the time and speeds applying to that specific wave. A standard voice procedure is used that reduces voice transmissions to a minimum while transmitting accurate positions to the waves. The procedure virtually eliminates the probability of “pyramiding” vectors to the waves. The system may also be used in the approach lanes and enroute from the parent ship or transport area to the rendezvous area or LOD provided frequencies are assigned that prevent interference. Boat waves or nonscheduled units may be guided effectively by this system during periods of darkness or reduced visibility. BEFORE DEBARKATION Before debarkation of the boats and amphibious vehicles of an amphibious assault, the BGC, all BWCs, and all wave guide officers are issued a gridded diagram of the boat lane to be used (see fig. 12-14). The diagram is an approximate picture of the boat lane from the rendezvous area to the beach. Longitudinal lines in the diagram divide the lane into three sections: L (left), C (center), and R (right). Left and right sections are each 40 percent of the total width; the center section is 20 percent of the total width. Lateral lines are drawn at 200-yard intervals along the lane and are numbered to indicate distance to go in hundreds of yards. Lane positions are described by a letter (L, C, or R) followed by a number of one or two digits. Positions outside the lane are indicated by a double letter: RR or LL. Time lines should be plotted on the grid overlay by the following method: Using the given wave speed of advance (SOA) and touchdown time, determine LOD crossing time for that wave. For the final l,000-yard transit, waves will be making battle speed (BS); therefore, count backwards from touchdown time to the BS line, accounting for the complete time (whole minutes and fractions). Divide the time from LOD to BS, again accounting for every whole minute and fraction. Label all times on the boat lanes blank, as shown in figure 12-14. When more than one wave is being controlled, the time clock will be divided into four primes: Prime Time (Seconds) Waves Marked 0 52 l/2 to 07 l/2 1, 5, 9 1 07 l/2 to 22 l/2 2, 6, 10 2 22 l/2 to 37 1/2 3, 7, 11 3 37 l/2 to 52 l/2 4, 8, 12 If the 15-second primes for grid construction (and grid position transmission) are used, the complete time for the transit can be accounted for. The control party has the gridded boat lanes plotted to scale in CIC, one lane for each wave to be tracked and controlled, to minimize confusion and obtain a clear and concise picture of the movement of each wave. RENDEZVOUS AREA In the rendezvous area, boats should be provided navigational assistance to keep the waves in their rendezvous circles. In addition, CIC tracks the waves and fixes the position of each wave on the grid upon the departure of the waves from the rendezvous area. The control party then transmits the position to the BWC by flashing light or by voice radio. The BWC, on receipt of a grid position that indicates the wave is 12-18