Yeah, some clarification is in order.
When we have to make an assumption about depth we use our knowledge of the type of contact we are tracking and the operations he is doing to put us in the ballpark. We generally don't know depth until the torpedo sends that data back to us. That is not always the case, but it is a good percentage of the time.
The good news is that we don't NEED depth for TMA. TMA falls under what FT's call SWAG (Sophisticated Wild-*ssed Guess). We make a lot of assumptions just to make the math manageable, such as:
Both contacts are at the same depth.
O/S maneuvers are intantaneous.
The ocean floor is perfectly flat.
This gets us "close enough," which in undersea warfare is really all you need. This isn't like WWII where you're shooting on gnats-*ss short range corrected intercepts; our goal here is to use relative motion to stay safe (ie is he far enough away from us that we're in our comfort zone), as well as to use the employment of 'advanced corrected intercept' tactics (which ask the question, "Can my weapon find him?") As weapons get better, solutions become less important (though a good solution will always be a vital fundamental).
In short, we don't need to know his depth. There are times when we will use his expected depth BAND to help our tactical situation (ie if you're shooting at a sub that is not at PD in a high contact density area, set a low ceiling for your weapon), but for TMA itself depth isn't much of a concern.
Could a more accurate bottom depth and contact depth help us with DE and bottom-bounce ranges? YES, but it's a difference that is small enough not to worry about. 4,752 yds is still 2.5 miles...close enough.
Remember what my old chief used to tell me guys, "close enough for the girls we go out with."
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