seafloor. When the doors encounter a cable, the cable is often snagged 

 and broken. No reasonable amount of armoring or mechanical protection 

 can protect the cable. Since cable repairs cost in the vicinity of $300K 

 per repair and because the number of cable failures is increasing at a 

 rapid rate, the economic justification for reducing cable vulnerability 

 is clear. In addition, the strategic and operational value of military 

 cable systems provides further incentive to solve this severe problem. 



For the last 25 years, telephone and electric utility companies 

 have been burying their service lines on land to protect them from 

 the elements and provide more reliable service to their customers. As 

 the number of transoceanic cables increased and the incidence of damage 

 to the cables became unacceptable, the Bell Telephone System decided that 

 burial of cables in the seafloor might protect these cables from damage 

 as it did on land. In 1966, the first Sea Plow was developed. It was found 

 that damage to cables buried by this and later Sea Plows was all but elim- 

 inated. Burying cables in the seafloor effectively removes them from the 

 primary hazard, bottom fishing, as well as current -induced motions and 

 anchor drag for all but deeply penetrating anchors. 



The Sea Plow is a large platform, mounted on skids, with a plowshare 

 and cable guide mechanism penetrating into the seafloor. The plow, which 

 is towed from the surface, is an uncomplicated piece of machinery, but 

 it suffers from a number of deficiencies that makes it unacceptable for 

 military cable installations. 



Depth: The existing plow is limited to 500 fathoms. This depth was 

 adequate to protect cables against traditional food fishing, but overfish- 

 ing and new markets, such as fish meal, fertilizer, and high protein animal 

 meal, are driving trawlers to 1,000 fathoms. 



Surface Support: Only two vessels are capable of providing the support 

 services required by the plow (a Canadian and a French ice breaker /cable 

 layer) for the following reasons: 



a. The tow force required is as high as 100,000 pounds. This force, 

 coupled with the slow burial speed (1 knot) , requires large amounts of 

 power, bow and stern thrusters for ship control, and a sophisticated navi- 

 gation system. 



b. The newest plow (Sea Plow IV) weighs 23 tons; thus, the ship must 

 have a large-capacity over-the-side handling system. 



c. The plow can bury cables only while they are being laid, thus, 

 the ship must be a cable layer, carrying large amounts of cable. 



Repeater Burying: Sea Plow IV plows a 16 -inch- wide ditch at all 

 times so that repeaters may be buried. Since the cable requires only a 

 4-inch-wide trench, and repeaters occur only once every 20 miles, a 

 significant waste of energy is associated with this operation. 



Tvaffioability: Since the plow is mounted on skids, obstacles, 

 such as rocks, often cause the device to stall, and it must be recovered 

 and the operation restarted. Some cable, then, is left unburied. 



