and it could not progress further upslope due 

 to canyon narrowing. Owing to its high de- 

 gree of maneuverability, the DIVING SAU- 

 CER was able to extricate itself from this 

 situation; however, many of the less maneu- 

 verable submersibles might have been 

 trapped. 



Such topographic extremes can produce 

 acoustic shadows which interfere with any 

 acoustic link between submersible and sup- 

 port craft. DEEPSTAR 4000 had occasion to 

 enter a submarine canyon in the Gulf of 

 Maine where the walls were so steep that 

 signals from its pinger could not be heard on 

 the surface. Consequently, tracking could 

 not be maintained, and the dive was aborted. 



Visibility: The lack of long range visibility 

 and the limited number of viewing ports can 

 bring the submersible into contact with all of 

 the hazards mentioned heretofore. In tropic 

 and sub-tropic waters, beyond the influence 

 of terrestrial run-off, long range horizontal 

 visibility exceeding 200 feet is possible. This 

 is an optimum condition, however, and is not 

 common. Beyond the limits of ambient light, 

 30 to 50 feet of lateral viewing with artificial 

 light is average. 



Even at a speed as low as 1 knot, only 30 

 seconds are available at 50-foot viewing 

 range to detect, identify and respond to 

 bring the vehicle to a halt. 



Organisms: It is impossible to evaluate the 

 over-all reaction of marine organisms to our 

 invasion of their domain and to identify all 

 those forms which represent some degree of 

 hazard. 



Over the past 50 years military subma- 

 rines have logged countless hours in every 

 body of water on this planet without encoun- 

 tering any significant threat from marine 

 life. However, due to the difference in size 

 and depth range, this experience cannot be 

 related directly to submersibles. A good ex- 

 ample is an attack made on ALVIIS in 1,800 

 feet of water by a 250-pound swordfish with- 

 out any obvious or intentional provocation 

 on the part of ALVIN. The swordfish' s bill 

 wedged in the fiberglass superstructure of 

 ALVIN on the first charge (Fig. 13.6) thus 

 preventing him from pursuing his attack. 



No damage was done to ALVIN, and later 

 everyone enjoyed a swordfish dinner. But, it 

 is possible that electrical wires or oil lines 



could have been severed thus creating seri- 

 ous problems. A port could have been dam- 

 aged through impact from a head-on encoun- 

 ter. Whether this was a "maverick" reaction 

 or a characteristic reaction to small sub- 

 mersibles is not known. BEN FRANKLIN 

 also experienced a swordfish attack during 

 its Gulf Stream Drift Mission, but with less 

 dramatic results. 



A passive but no less potentially danger- 

 ous form of marine life, is the giant kelp. It is 

 quite possible that a submersible penetrat- 

 ing a kelp "forest" could become so entan- 

 gled that return to the surface would be 

 impossible. This threat is compounded by 

 redueed visibility caused by heavy growth. 



Wh^en swimmers are used to support 

 laun(;h/retrieval, the threat from dangerous 

 marine animals is compounded. Some of 

 these threats are obvious in the case of 

 sharks, but less obvious where Sea Wasps or 

 othe^ stinging coelenterates are concerned. 



Miscellaneous: During Operation on the Blake 

 Plateau in 2,500 feet of water ALUMINAUT 

 was traveling at 5 feet above the bottom and 

 approached a large hole. Over this hole the 

 vehicle descended although the 100-pound 

 negative buoyancy had not been modified by 

 the pilot. At least 1,000 pounds of steel shot 

 had to be dropped before ALUMINAUT could 

 stop its descent. Since no bottom current, 

 which could have pulled the vehicle into the 

 hole, was evident, the cause of descent was 

 ascribed to fresh ground water seepage out 

 of the hole which created a less dense water 

 patch within the cavity. Although this is 

 supposition by the crew, the fact remains 

 that ALUMINAUT did descend, and marine 

 fresh water aquifers are known to exit under 

 the ocean along parts of the Atlantic coast. 

 How widespread and prevalent such sub- 

 aqueous aquifers may be is a matter of con- 

 jecture. A similar buoyancy change was said 

 to have occurred when ALUMINAUT tra- 

 versed the mouth of a large river off Connec- 

 ticut. 



Man-Made Hazards 



Cables: Submarine cables represent a dan- 

 ger of entanglement to the submersible. 

 While the cable's route may be known, its 

 configuration on the bottom can be in snarls 

 or it may be suspended off the bottom as it 



632 



