INTRODUCTION TO SONAR 



Mines 



Navy mines are thin-cased underwater weap- 

 ons with a heavy load of high explosives. They 

 may be laid by both aircraft and surface craft, 

 but submarines are employed for mine laying 

 when secrecy is required, or when the area to 

 be mined is beyond the range of aircraft. Mines 

 may be of the bottom, moored, or drifting type. 

 Bottom mines rest on the ocean floor, and are 

 highly effective in shallow water. Moored mines 

 are positively buoyant. A cable, attached to an 

 anchor on the sea bottom, holds the mine at a 

 predetermined depth beneath the surface. Drift- 

 ing mines float freely at or near the surface. 

 Mines may be actuated by contact with a vessel, 

 by a vessel's magnetic field, by noise, or by 

 pressure differences created when a vessel 

 passes over the mine. Acoustic-, pressure-, and 

 magnetic-influenced mines may be set to permit 

 the passage of several ships, then explode under 

 the next one to pass over. 



Missiles 



Specially designed fleet ballistic missile sub- 

 marines, as mentioned earlier, carry the Polaris 

 missile, adding tremendous striking power to the 

 submarine fleet. The latest Polaris model, the 

 A3, has a 1-megaton nuclear warhead, with a 

 range of 2500 miles. An improved Polai'is, called 

 the Poseidon, will have the same range as 

 Polaris, but double the payload, with multi- 

 ple warheads to confuse enemy defense sys- 

 tems. 



MANEUVERABILITY 



Modern nuclear submarines present a serious 

 problem to antisubmarine (A/S) forces. Holddown 

 tactics used to force conventional submarines to 

 surface or snorkel to recharge batteries, are 

 ineffective against nuclear submarines because 

 they do not use batteries for submerged opera- 

 tions. They can remain submerged on nuclear 

 power for indefinite lengths of time. The attack- 

 type submarines are faster when submerged than 

 on the siirface. Moreover, they exceed the speeds 

 of many types of surface ships. Their sail- 

 movmted diving planes permit radical maneuvers, 

 almost like those of an airplane. Actual operating 

 depths are classified, but the modern submarine 

 can go considerably deeper than the World War 

 II types. 



ANTISUBMARINE UNITS 



Antisubmarine (A/S) forces are composed of 

 special design ships, aircraft, and submarines. 

 Their purpose is to seek out and destroy enemy 

 submarines. Aircraft carriers of the CVS tj^e 

 (with fixed-wing aircraft and helicopters em- 

 bai'ked), together with a number of destroyers, 

 form hunter-killer (H/K) groups, whose primary 

 mission is to deny an enemy the effective use 

 of his submarines. Guided missile destroyers, 

 whose chief function is defense against air 

 attack, also have A/S capabilities. Nuclear at- 

 tack submarines ai'e also assigned to H/K groups. 

 The SSNs are especially effective in A/S opera- 

 tions because of their ability to select the depth 

 providing the best sonar conditions, their long 

 endurance and maneuvering capabilities, and 

 the type of weapons they carry. Elements of a 

 typical himter-klller group are shown in figure 

 2-5. 



SHIPS 



The destroyer-type ships (DDs) are the prime 

 submarine hunter-killers. They operate in H/K 

 groups, screen convoys, carriers, and other naval 

 vessels against submarine attacks, and provide 

 protection against air attack. 



Destroyers range in size from 2100 tons to 

 nearly 8000 tons displacement. From about 5000 

 tons up they usually are designated frigates (DLs). 

 Destroyer escorts (DEs) are somewhat sm.aller 

 than regular destroyers, although the latest tjrpe 

 of escort is larger than many World War 11 

 destroyers. Ships with guided missile capability 

 have the letter G added to their designation 

 (DDG, DLG, DEG). 



Antisubmarine armament carried by frigates 

 of the type shown in figure 2-6 consists of 

 ASROC (antisubmarine rocket), located behind 

 the forward missile launcher, and A/S homing 

 torpedoes amidships on each side. Some of the 

 latest DLGs fire ASROC and Terrier missiles 

 from the same launcher. 



Guided missile destroyers have essentially 

 the same A/S armament as frigates. Thearrange- 

 msnt varies between classes. Some DDGs have 

 the ASROC launcher forward, behind the 5"/54 

 gun; others have it amidships, as seen in figure 

 2-7. 



Conventional destroyers (DDs) that have 

 undergone the fleet rehabilitation and moderniza- 

 tion (FRAM) program have either ASROC or 

 DASH, in addition to their A/S torpedoes. (The 



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