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In order to learn how sonars work in CMO and to derive ASW and submarine tactics from it, I‘ve made a test scenario. Some results are plausible to me some less. I am not posting in Tech Support because I am not sure if bug or whether there is a physical effect behind it. Probably some submarine or ASW experts can explain.
I made various setups with ships and submarines in various depth. The ships either are stopped o rare sailing. The ships are using either hull sonar only, active sonar or variable depth and hull sonar in common. The submarines cruising towards the ships in shallow, just-over-layer, witihn-layer, just-under-layer and deep as possible.

Here are the results for stopped ships: Here for sailing ships: Things I’ve learned:
- If ship has only hull sonar or active sonar, best place for subs is under the layer and deeper and shallow is worst.
- If ship uses variable depth sonar, best place for subs is within layer, worst place is under the layer in convergence zone and shallow in close range
- Question: In close distance it seems VDS have no advantage to hull sonar – is this to be expected?
- The use of active sonar turns passive sonar off.
- Question: Is this really the case IRL? Can’t the frequency of active sonar have filtered out?
- active sonar is always worse than passive sonar, except if pinging ship is fast and sub is very deep. The only reasonable situation to use active sonar is to get an exact range fix after the sub has been spotted by passive sonar already. (!?)
- For search results it makes no difference if a ship stops or is creeping around.

Things I am wondering about:
- There is a lot of findings at 12.8ish in shallow waters and 9.8ish in deeper water regardless how loud the sub is. Is this to be expected? For me it looks like CMO is using fixed thresholds for detection rather than calculations.
- See picture below. The outer convergence zones are from 27 – 32 nm respectively 56,5 – 61, nm. When a sub was detected picking up and loosing fitted quite well with that. The inner sonar zone has a radius 22,3 nm. Regardless how loud a submarine was, it never managed to detect a submarine further away than 12.8 nm. The range from 13 – 22 nm seems to be blind.

I'm totally crazy about ASW aspect of Command, and here are some my comments...

- There is a lot of findings at 12.8ish in shallow waters and 9.8ish in deeper water regardless how loud the sub is. Is this to be expected? For it looks like CMO is using fixed thresholds for detection rather than calculations.
- See picture below. The outer convergence zones are from 27 – 32 nm respectively 56,5 – 61, nm. When a sub was detected picking up and loosing fitted quite well with that. The inner sonar zone has a radius 22,3 nm. Regardless how loud a submarine was, it never managed to detect a submarine further away than 12.8 nm. The range from 13 – 22 nm seems to be blind.

Yes, there is range thresholds for direct path sonar detection, normally 9.5nm (20,000 yards, see p.304 of manual).

With surface duct effect, this range and sonar perfomance can increase if searcher (or sonar) and target is both at shallower than -50m (-165ft). This is why, at shallow (-40m/131ft) TA range suddenly increased to 12.8nm aganst other 9.8nm.
(https://www.matrixgames.com/forums/view ... 1&t=394043)

Beyond direct path maximum range is shadow zone, and you cannot detect target no matter how loud it is, with exception of Convergence Zone.

- Question: In close distance it seems VDS have no advantage to hull sonar – is this to be expected?

Because of direct path threshold, TA does not mean it can detect target at 17-25nm for example. However, TA generally has more max range (this means TA can use one or more CZ: this is prominent for early cold war ships which hull sonar range is generally less than 15nm) and less affected by platform speeed than Hull sonar.

- active sonar is always worse than passive sonar, except if pinging ship is fast and sub is very deep. The only reasonable situation to use active sonar is to get an exact range fix after the sub has been spotted by passive sonar already. (!?)

Remember, active sonar performance is greatly affected by target aspect, or apparent angle from searcher. If target is really quiet (imagine fully stoped diesel sub) and showing 45-135 degree broadside to searcher, active sonar range can surpass pasive.

lumiere wrote: Sun Nov 26, 2023 2:59 pm I'm totally crazy about ASW aspect of Command, and here are some my comments...
...
Yes, there is range thresholds for direct path sonar detection, normally 9.5nm (20,000 yards, see p.304 of manual).
...

Hmm, this may explain the strange SOSUS behaviour. Here and here.
SOSUS somehow detects distant subs, but when the conditions for CZ are not met, it expects the contact within 9.5 nm range due to the threshold.

lumiere wrote: Sun Nov 26, 2023 2:59 pm
Yes, there is range thresholds for direct path sonar detection, normally 9.5nm (20,000 yards, see p.304 of manual).

With surface duct effect, this range and sonar perfomance can increase if searcher (or sonar) and target is both at shallower than -50m (-165ft). This is why, at shallow (-40m/131ft) TA range suddenly increased to 12.8nm aganst other 9.8nm.
(https://www.matrixgames.com/forums/view ... 1&t=394043)

Beyond direct path maximum range is shadow zone, and you cannot detect target no matter how loud it is, with exception of Convergence Zone.

Then it's IMHO a bug. The inner range circle visualisation represents the values of DB but the hardwired code works differently. This is at least misleading.

That's why from v1.05, transparent direct path circle is rendered around the sub. Problem is that, when CZ is not available (the very moment you could rely DP detection only), this circle will also gone.

It would be nice if this circle will always rendered or underwater sensor range ring is shrinked to DP range under no-CZ environment (should I post this at feature request?).

Quark73 wrote: Mon Feb 12, 2024 7:19 am

lumiere wrote: Sun Nov 26, 2023 2:59 pm
Yes, there is range thresholds for direct path sonar detection, normally 9.5nm (20,000 yards, see p.304 of manual).

With surface duct effect, this range and sonar perfomance can increase if searcher (or sonar) and target is both at shallower than -50m (-165ft). This is why, at shallow (-40m/131ft) TA range suddenly increased to 12.8nm aganst other 9.8nm.
(https://www.matrixgames.com/forums/view ... 1&t=394043)

Beyond direct path maximum range is shadow zone, and you cannot detect target no matter how loud it is, with exception of Convergence Zone.

Then it's IMHO a bug. The inner range circle visualisation represents the values of DB but the hardwired code works differently. This is at least misleading.

Not sure what you mean here. Can you please elaborate on the inconsistency?

lumiere wrote: Mon Feb 12, 2024 8:23 am That's why from v1.05, transparent direct path circle is rendered around the sub. Problem is that, when CZ is not available (the very moment you could rely DP detection only), this circle will also gone.

It would be nice if this circle will always rendered or underwater sensor range ring is shrinked to DP range under no-CZ environment (should I post this at feature request?).

That's a good suggestion, will see what we can do.

Dimitris wrote: Mon Feb 12, 2024 11:24 am
Not sure what you mean here. Can you please elaborate on the inconsistency?

Well, the picture in opening post shows a circular area with approx. 22 nm radius for direct path detection. The measured detection range was either 12.8 resp. 9 nm or less. If I got @lumiere right, around 13 nm is pretty much the max range possible.
The inconsistency for me is, that CMOs UI suggests a possible sonar detection range of 22 nm, but only 9 or 13 nm are feasible.

From Build 1307.10 release notes

* FIXED: [B1307.9] Surface duct effect (sonar) persists at deeper depths (Ref: https://www.matrixgames.com/forums/view ... 0&t=393911 ). Tweaked this so that the benefit of surface ducting begins (very slightly) at 50m depth and increases in percentage as the sensor and/or the target nears the surface. The maximum benefit (1.5x of nominal direct-path range) happens only when both the sensor and the target are on the surface.

So, 22.5nm DP range is possible at surface (15*1.5=22.5). However, even least intelligent sub skipper may know too well that surfaced submarine will be first spotted by radar or visually.

Then it's academically [WAD]. Case closed for me.