NAVAL IMPORTANCE OF WAKES 



443 



Figure 2. Wake of USS Moale (DD 693) at 16 knots from 2,500 feet. 



or identifying the ship which has produced the wake. 

 Such utilization of wakes in offensive operations com- 

 prises visual detection from the air and thermal de- 

 tection from surface ships or submarines, as well as 

 acoustic detection. However, the present discussion 

 is concerned only with the acoustic properties of 

 wakes and the importance of these acoustic proper- 

 ties in naval warfare. 



Acoustic interference produced by wakes is fre- 

 quently encountered in the operation of sonar gear. 

 False echoes from submarine wakes may confuse the 

 sonar operator on an antisubmarine vessel and may 

 even lead to an attack on a wake knuckle, a dis- 

 turbance in the water when a submarine suddenly 

 speeds up and turns sharply, while the submarine 

 escapes. During thirty imsuccessful attacks on sub- 

 marines by United States antisubmarine vessels in 

 1944, where the presence of a submarine was ascer- 

 tained but no damage inflicted, 12 per cent of the 

 failures were attributed to attacking wakes, a larger 

 percentage than assigned to any other single cause. 



Wakes laid by surface vessels can also be disturb- 

 ing in antisubmarine warfare. After one or more at- 

 tacks in an area, echoes from old wakes from surface 



ships can be confusing. Moreover, a moderately fresh 

 wake is highly absorbent and may shield a shaUow 

 target on one side of the wake from detection by a 

 surface vessel on the other side. In fact a projector 

 surroimded by a fresh wake is almost completely 

 useless, since very little sound can escape through the 

 wake. Thus a surface ship will commonly find that 

 its echo-ranging equipment "goes dead" when the 

 ship passes through a fresh wake. 



Harbor detection equipment can also be seriously 

 hampered by the presence of wakes. When a de- 

 stroyer at moderate speed passes in the neighborhood 

 of bottom-moimted supersonic listening gear, ships 

 passing by subsequently cannot be heard for some 

 time. Similarly, sneak craft in the wake of a large sur- 

 face vessel are very difficult to detect by echo rang- 

 ing. To reduce the seriousness of these effects in 

 combating submarines, or to use them most effec- 

 tively in submarine warfare, accurate information is 

 required on the reflection and absorption of sound by 

 wakes under different conditions. 



The use of wakes in offensive operations against 

 the wake-laying vessel is a relatively new field. As an 

 exampile of this utihzation of wakes, it was at one 



