VISUAL SYSTEMS OF TRANSIENT COMMUNICATION 



261 



discrimination render them treacherous at 

 best. Spatial patterning of visual stimuli, 

 such as that suggested above for blinker, is 

 employed in the signal flag, but this advan- 

 tage is reduced radically by the difficulty, 

 noted above, of making the pattern effective. 

 Signal flags may persist as a colorful, oc- 

 casionally convenient, and historically in- 

 teresting system, for certain types of per- 

 sistent communication, but they have no 

 place in transient communication. They 

 are relics of an earlier age. 



Semaphore 



Semaphore signalling is essentially sup- 

 plemented and formalized gesture. Its 

 greatest merit rests in the simplicity of the 

 equipment needed, and, indeed, the dis- 

 pensibility of any equipment at all in emer- 

 gencies. However, like all the direct meth- 

 ods of communication, except blinker, it is 

 not effective over any useful range without 

 the use of visual aids by the receiver. 



Mediate Systems 



The second major class of visual com- 

 munication systems is the mediate system. 

 Mediate systems vary considerably in com- 

 plexity of equipment and in flexibility. The 

 simplest of these systems have borne a great 

 similarity to the direct methods. They are 

 dependent upon an unobstructed optical 

 pathway between sender and receiver, and 

 the display is seen through a large column 

 of atmosphere. In the more complex pro- 

 cedures, proximate stimulation of the re- 

 ceiver is employed. 



Sea Dyes 



The simplest mediate visual system is the 

 use of dyes, usually fluorescent, dissolved 

 in the sea, which serve to signal the receiver 

 of the presence of a sender in the vicinity of 

 the highly colored water which results from 

 release of the dye. Sea dyes were developed 

 for, and have been used most extensively in, 



air-sea rescue work.^ Obviously, this type 

 of mediate system is inflexible. The signal 

 is either present, or not, so that no very pre- 

 cise control of a receiver can be exerted 

 through such a simple variation in the stimu- 

 lus. However, in the sea-dye, we may have 

 a method of visual communication which 

 can be useful for recognition signalling by 

 submarines. In air-sea rescue work, com- 

 munication at maximum range is desired, so 

 that the color of the dye has been deter- 

 mined by the relative visibilities of dyes of 

 different color. In recognition signalling, 

 however, the signals are seldom if ever given 

 or required at maximal visual range, so that 

 this variable is no longer important. It is 

 suggested, therefore, that the use of fluores- 

 cent dyes of different colors, released into 

 the sea in various spatial patterns, be seri- 

 ously considered as a possible solution to the 

 problem of the recognition of submersibles 

 by air craft. Several advantages over cur- 

 rent procedures of recognition signalling are 

 evident. (1) Sea dyes are relatively invisi- 

 ble to surface vessels, although they are con- 

 spicuous to aircraft. (2) Areas of dyed 

 water are conspicuous and easily identified 

 by friendly properly briefed pilots. Since 

 recognition signals will be given only when 

 the behavior of an aircraft indicates to the 

 commanding officer of a surfaced or snorkel- 

 ling submarine that his ship has been seen, 

 and since an unfriendly aircraft will at- 

 tack, signal or no signal, such signals should 

 achieve their stated purpose, the prevention 

 of attack by friendly aircraft, without risk 

 of the misinterpretation of a flare or light- 

 flash as gunfire, and without revealing the 

 presence of the submarine to all surface craft 

 within visual range. (3) Sea dyes cannot 

 be mistaken for gun fire, as is the case with 

 other methods of visual recognition, such as 

 blinker and flares. (4) By dispersion of dye 

 particles of the proper size, dyeing can be 

 produced rapidly, and may also be effective 



^ The use of colors on life rafts and jackets, 

 and of cloth panels, for the same purpose, is per- 

 haps yet another method of communication. 



