OCEAN ELECTRONIC NAVIGATIONAL AIDS 9 



Loran has already played a prominent role in rescue operations. Distress 

 at sea usually occurs during foul weather when determination of position by 

 celestial observations has been impossible for several days. Under such limi- 

 tations, the distressed vessel's dead reckoning position may be considerably 

 in error. 



In the Aleutian area, a distress case occurred which illustrates the value of 

 Loran in the saving of life at sea. Surface vessels and aircraft were engaged 

 in search operations for a barge foundering in heavy seas with eight 

 persons aboard. Positions transmitted by radio from the barge, 24 hours 

 apart, were hundreds of miles different though the craft was not under power. 

 This indicated that she did not have a reasonably correct knowledge of her 

 position, and rescue operations were fruitless. After transmission of the 

 Loran-determined position to surface vessels, the distressed craft was located 

 and all hands rescued in a matter of hours before the water-filled barge sank 

 during 70 miles-per-hoiu" winds. 



Thus Loran, through the medium of electronic science, constitutes a 

 fundamental supplement to other methods of navigation, in assisting and 

 protecting lives and property at sea. 



CONTROL OF LORAN TRANSMISSIONS 



Since the value of the Loran system is equal only to the accuracy of timing 

 of the signals transmitted, every precaution is taken to safeguard the func- 

 tioning of the system. This is effective to such an extent that the navigator 

 may feel certain that the Loran data which he obtains is correct. This fact 

 has been proved by the acid test of completely successful Loran operation 

 under the most severe conditions. 



The nature of Loran transmitting station equipment makes it necessary 

 for the Loran transmitting station operator to observe the signals of both 

 stations continuously during transmission. As a consequence, the man on 

 watch at either station of a pair is in a position to "double check" for the 

 existence of any fault that might occur in the signal of either station. 



Loran transmissions can be momentarily at fault due to many possible 

 causes such as electrical failure of a part of the equipment or operating error 

 in manipulating controls. Even though these troubles may be minor and 

 of relatively short duration, it is essential that the navigator be acquainted 

 with the failure instantly and positively. In order to do this, a blinker device 

 is switched in at either of the two stations. "Blinking" produces a charac- 

 teristic movement of the transmitted signals, which is easily recognizable and 

 serves to warn the navigator that the signals are not to be used for naviga- 

 tional purposes until the "blinking" ceases. 



In the event the failure is sufficiently serious to prevent transmission en- 

 tirely from one of the paired stations, it would not be possible for the navi- 

 gator to misinterpret the Loran signals, inasmuch as the presence of only 

 one of the expected signals on the air would preclude making any time dif- 

 ference measurements at all from that particular pair. Other pairs would 

 not be affected. 



Because of the fundamental checks which are vigilantly maintained on the 

 transmitted Loran signals, the navigator at sea or in the air is assured that 

 any transmissions which he receives, with the exception of "blinking" signals, 

 are accurate, reliable electronic guideposts marking the lines of positions of 

 this modern long-range navigational aid. 



TRANSMITTING STATION FUNCTIONS 



Because Loran is concerned with the measurement of radio signals from 

 two different sources, Loran stations operate in pairs. The function of each 

 station of a Loran pair is somewhat different from that of its companion 

 station, and each is given a designation which is descriptive of the role which 

 it performs, namely, "master" station and "slave" station. 



The "master" starts the cycle of transmission by sending out a pulse of 

 radio energy which is radiated in all directions including that of both the 

 navigator and the "slave" station. After traveling the distance between the 

 two transmitting stations, known as the "baseline," the pulse transmitted by 

 the "master" arrives at the "slave." This signal is received by means of the 

 Loran equipment of the "slave" station and the time of its arrival is used by 

 the "slave" as a reference for the transmission of its own signal. 



