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Limiting Lines of Submerged Approach (LLSUA)

This is a discussion on Limiting Lines of Submerged Approach (LLSUA) within the Military Strategy and Tactics forum, part of the Global Defense & Military category; Limited line of submerged approach.Would any of you care to explain this to me?...


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Old April 30th, 2006   #1
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Limiting Lines of Submerged Approach (LLSUA)

Limited line of submerged approach.Would any of you care to explain this to me?
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Old May 2nd, 2006   #2
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There must be some submariner or naval operations analyst who can explain this
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Old May 2nd, 2006   #3
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Actually there really is no simple answer as there are a lot of variables.

Fundamentally its an issue of "encouraging" an enemy sub to take an alternative route to a nominal target due to various impediments. eg
  • submarine geologies (underwater canyon/trench, shelf, biologics etc...)
  • seabed arrays
  • mines
  • own forces setting up a killbox (eg HK team presence)
  • aggressive patrolling, (be it sub, skimmer, air etc...)
By encouraging the sub to take an alternative and possibly more circuitous route you can also set that sub up for interception at likely waypoints of your choosing.

By limiting the approaches it also enables you to set up and focus your own ASW or ISR forces in a place more of your own choosing.
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Old May 2nd, 2006   #4
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How do you spell LFA ? I say screw the whales!
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Old May 2nd, 2006   #5
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How do you spell LFA ? I say screw the whales!
The whales have got better LFA anyway I would think. Isn't the sperm whale able to hit 45 knots? You have to know the rules of the road at that speed..
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Old May 2nd, 2006   #6
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Originally Posted by gf0012-aust
The whales have got better LFA anyway I would think. Isn't the sperm whale able to hit 45 knots? You have to know the rules of the road at that speed..
Yep, and if I had to pick between a bunch of whales and our sailors and marines......well then...... hit your nearest beach while the meat is fresh. Frankly I cant believe we are even having this controversy. Goes to show you how many veterans or active service types populate the great thinkers of our Universities, and their families.

But I digress.....back to topic.
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Old May 3rd, 2006   #7
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I was under the impression it is something to do with ageometric angle and the speed of the target
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Old May 3rd, 2006   #8
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Originally Posted by Truculent
I was under the impression it is something to do with ageometric angle and the speed of the target
not that I know of. it may well be, but I've only ever heard of it in ref to establishing a posture.
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Old May 3rd, 2006   #9
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gf0012-aust,would you be able to provide any open reference material to your answer?
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Old May 6th, 2006   #10
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Originally Posted by Truculent
gf0012-aust,would you be able to provide any open reference material to your answer?
Sorry for being tardy in reply. have been a little busy offline.

Unfort no. The last ref I had re it was at an Underwater Defense Technology Conf I attended in Hawai'i in 2004. It was part of a discussion session being run during the Conf so was sans "notes".

It was mentioned as an adjunct to some Safe Harbour discussions and marine based anti-terrorism/sub warfare issues.
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Old October 9th, 2008   #11
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Limited line of submerged approach.Would any of you care to explain this to me?
Has to do with where a submarine must be to be able to get within firing range at a given speed for a given target speed. if you picture a vector of target speed , draw a circle around it with a radius equal to weapon range. then two lines tangent to that circle that are displaced from the direction of the target speed vector by an angle defined by: angle = arcsine (submarine speed/target speed). If the submarine isn't between these two lines (they extend to infinity) at the begining of the problem, then it can never reach firing range at that speed if the target remains on the same course and speed. One of the reasons no ship travelling over 20 knots was torpedoed in WWII.
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Old October 14th, 2008   #12
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Old December 4th, 2008   #13
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jhpatton is spot on. The submarine has a limited speed at which it can approach (say 10 knots). The target is travelling at say 20 knots. Obviously, if the sub is astern, it can never catch up to reach a firing range. If it is right ahead, it only has to sit and wait. As its start position moves further towards either beam of the target, the sub has to approach at faster and faster speeds in order to reach a firing range (the torpedo danger zone) where the target speed and torpedo speed will result in the torpedo successsfully hitting the target. There is a point on either beam where the submarine must approach at 10 knots to just make it into the TDZ to fire at the last moment before the target passes (called point target). The limiting lines of submerged approach are (as patton says) the limits where the sub at 10 knots (or other speed limit) can steer a course to reach point target. If it starts outside these lines, it is physically impossible to reach a firing position without going faster than 1o knots (and the risk of detection, depleted battery etc). If the target becomes aware of the submarine's position, a simple alteration of course to place it outside the LLSuA will prevent it from ever reaching a firing position.
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