to assist the operator in homing. At times 

 the very simplest means have been used — 

 e.g., following the marks or trail the sub- 

 mersible left in the sediment on a previous 

 dive, following a cable or visually tracking a 

 trail or pattern of debris, as did TRIESTE II 

 in the SCORPION operations. On the other 

 hand, the target itself may produce a scour 

 mark which may be used for homing — e.g., 

 the H-bomb lost off Spain. In this situation, 

 ALVIN followed a likely looking trail which 

 led directly to the bomb. Often there are no 

 alternatives to such homing methods, but 

 there are other more dependable approaches 

 which are commercially available and offer 

 better performance than mere chance or ser- 

 endipity. These are: Marker buoys and pas- 

 sive and active sonar targets. 



Marker Buoys: 



The simplest homing system is an an- 

 chored buoy line which either the submers- 

 ible or surface ship plants at the desired 

 location. The concept is deceptively simple: 

 The operator needs only to follow the line 

 down to the anchor. But, limited water visi- 

 bility, restricted submersible viewing capa- 

 bility, currents and limited maneuvering 

 ability all may work individually or together 

 to thwart this most fundamental approach. 

 Furthermore, adverse weather can move the 

 buoy and its anchor or simply tear it loose. 

 In reality, this method serves mainly as a 

 visual aid to positioning the surface ship 

 and, subsequently, the submersible, once it is 

 in close approximation to the undersea target. 



Obviously, there are many methods of 

 planting a buoy, the time-honored one being 

 simply to lower an anchored line to the bot- 

 tom and buoying it off on the surface. The 

 drawback to this method is that the ship 

 drifts off the chosen site while the anchor is 

 being lowered. A more exact and quicker 

 approach is offered in the Helle "Call Buoy" 

 (Fig. 10.27). 



ing in on a ping emitted from the target or b) 

 interrogating a transponder which marks 

 the target and homing in on it from the 

 range and bearing data thus obtained. 



The arrangement and deployment of re- 

 flectors, pingers and transponders vary ac- 

 cording to the vehicle's onboard capabilities 

 and the nature of the task. Deployment of 

 these devices may be from the surface ship 

 or from the submersible itself. The devices 

 may be used individually, or they may be 

 combined into an array as shown in Figure 





Fig 10-27 The Helle "Call Buoy " The cylinder on the nght is dropped over the side 

 and sinks to the bottom For up to 3 years after installation, a coded release signal 

 from the command module (left) will cause the cylinder to separate and a buoy to nse 

 to the surface while unreeling a cable The Call Buoy is presently available with 700 ft 

 of cable. (Helle Engineenng Inc) 



Passive and Active Acoustic Targets: 



The most successful homing devices utilize 

 acoustics either 1) passively, by pinging off a 

 sound reflecting object and determining its 

 bearing relative to the submersible (range is 

 not necessarily important, but may be desir- 

 able), or 2) actively, by a) receiving and clos- 



513 



