May 6, 200916 yr One of the purposes of this scenario was to have a submarine travelling at something faster than "crawl" speed, to see if it would be detected or not. I chose a T56 ASW ship because being a ASW type, i thought it might have a better chance to detect the sub. To make the submarine work (have to speed up) i placed it 20.0nm behind the T56 and had it chase down and get a visual (not just a sonar detection). Somewhere in the North Atlantic. Sea state 4. A french made T56 ASW patrol boat is steaming home. On board her sonars had picked up some new secret underwater sounds likely generated by an unknown nationalities new submarine. Its believed to be the first time the sound has been recorded. Using the hard copy tape, they (whomever "they" are) may be able to decipher and program their own sonars to pick up the sound again because they will know what they are looking for. It could be a profitable secret to sell on the open market. At intermediate depth I an LA Class submarine is plowing through the water at 20kts. Its mission is to close the gap on the T56 and monitor. Then wait for orders. Thats all she knows, its the usual story of "hurry up and wait". When the chase started the range is 20.0nm. The T56 is travelling at 12kts and the LA Class is at 20kts. The sub is catching the T56 at the rate of 8kts or 4.0nm each 30 minutes. Detection situation T56 ASW speed 12kts Active sonar 3.8nm and chance to detect her shadow, the LA class sub. 75% 0.8nm 50 2.1 25 2.9 LA class Submarine @ intermeadiate depth I and 20kts passive 3.8nm hull mounted sonars ability to detect the T56. 75% 1.5nm 50 4.2 25 5.7 Despite using a passive sonar, the LA Class has a better chance of detecting the ASW vessel T56 using its active sonar, mainly due to the LC Class's anechoic coating halving detection range otherwise chances would be even. Start of "the Chase" 0:00:0 range 20nm Plot T56 using homemade random movement table: no change (random movement table explained below) Range reduces to 16nm Detection not possible due to range 0:30:0 Plot T56 using homemade random movement table: no change Range reduces to 12nm Detection not possible due to range 1:00:0 Plot T56 using homemade random movement table: no change Range reduces to 8.0nm Detection not possible due to range 1:03:0 change to tactical turns due to detection ranges getting close. Plot T56 using homemade random movement table: no change Range reduces to 11.5nm Detection not possible due to range 1:06:0 Plot T56 using homemade random movement table: no change Range reduces to 11.0nm Detection not possible due to range 1:09:0 Plot T56 using homemade random movement table: no change Range reduces to 10.5nm Detection not possible due to range 6 more rolls made in quick succession to speeden up the game - the T56 does not change its movement. Range closes to 5.5nm Detection possible for the LA @ 25%. No result though. 1:15:0 Plot T56 using homemade random movement table: no change Range reduces to 5.0nm Detection possible for the LA @ 25%. No result. 1:18:0 Plot T56 using homemade random movement table: no change Range reduces to 4.5nm Detection possible for the LA @ 50%. And the passive sonar detects! Classification is 10% (base) + 20% (active sonar of T56) +5% (T56 speed) = 35% and the roll is 40! Close but no cigar. But the sub can determine its a French ship and is therefore their likely contact they need to shadow. (4.3.3) maintaining contact adds 15% to the detection roll. The LA sub Captain decides to draw within 4.0nm where there is a 65% chance of detection (50% + 15% for contact). This also means his sub is not detectable currently by the T56. A good distance to shadow from. 1:21:0 Plot T56 using homemade random movement table: no change Range reduces to 4.0nm Detection possible for the LA @ 65% is maintained. 1:24:0 Plot T56 movement: no change LA Class reduces speed to 12 kts now that they are at the required 4.0nm and will try and surface so i can use the periscope depth rules and try for an eyeball at the T56. This may change the detection possibility. Mmm, just came across cavitation possibilities but it looks like active sonars dont have a cavitation modifier. Submarine moves to periscope depth. Detection roll for LA Class @ 65% is maintained. Detection roll for T56 is unchanged and therefore not possible. Change to engagement turns (30 seconds) to use periscope. 1:24:5 1st move no change in speed thereby risking "Kelvin Wake" per (3.2.1.2). 1st fire: nothing Detect: sonar @ 65% is maintained. Visual sighting (4.5.1) says visual range from perriscope to small target is 6.0nm. The sub eyeballs the T56 and tries to identify the target (4.5.8) and is able to determine the type of ship as a T56. As per 4.5.4 there is a 20% chance the T56 see's the periscope and ... (die roll) they dont. 1:25:0 No change Back to tactical turns (3 minute) 1:28:0 T56 and there is a movement change (finally! I will explain my random table at the end). Speed increases (oh!) 1kt to 13kts (hardly worth the effort). But wait, theres more, direction change and the T56 is doubling back! Now we get interesting. I should have been writing down my Subs plot information before determining the T56 to accurately show the order of things. For instance, its no good me seeing the result of the random movement roll and then plotting sub movement after seeing the results, thats not how i have done it. I plot my subs movement and then i roll on the random movement table (your interested in this table, arent you? I've mentioned it enough ...!). LA Sub movement is unchanged because i plotted before knowing the T56's change of direction. Distance closes rapidly to 2.75nm as the sub is taken off guard and the T56 is now moving TOWARDS the sub. The sub cannot fire yet, but having made positive ID it is ordered to fire if a 1 is rolled on a D6 per tactical turn (i just made another random rule up). Rolling D6 now for OK to fire ... and a 1 is rolled! I was looking forward to seeing if the T56 could detect the sub and then changing my subs plotted movement to go all stealthy but now the orders through i can fire on her. Turn after turn of nothing happening and now its all happening at once. This homemade random table thingy is really working for me. The LA sub didnt plan any fire, so it cannot fire yet. Detection LA sub maintains sonar contact. T56 is now within range to try for the first time. It has a 25% chance and fails. Reaction fire ... let me consult the books ... Page 2-7 says i can fire homing torpedoes this phase but they do not move yet and ROF is halved, so i can only fire 1 this time. Time for some retrospective gaming. Before i can fire i need a TMA (6.1.2). This is something the sub likely would have done as a matter of normal business but i wasnt aware of it so i will make the rolls that should have been made now. I think its fair to say i would have got 2 x TMA rolls. Range was 4.0nm at 1:18:0 and TMA roll says ... 81, not even BOL. Second roll at 1:21:0 and TMA roll is 20 which equals a good TMA (the best there is). Haha "if target changes course (as it has before i got the fire order) i need to re-establish the TMA so i will roll again for the 1:28:0 TMA and 87 which is enough for a "fair" solution. Torpedo 1 is fired but does not move. Moving to engagement turns 1:18:5 1st movement for the LA. I wonder if i speed up to whiz past the T56 or at least close to him i am too close for him to fire at me (what if i whiz into an explosion if my Mk48 torpedo hits)? Or do i slow down/stop so i can fire from range? Quickly, i'm a sub commander, i dont have time to do the math!!! A torpedo is already in the water and is a chance to hit. The LA Class sub chooses to turn off 90 degrees and hope to loose itself again before sneaking up on the T56 and getting a good target solution before firing. The sub has time to engage later, why rush it? 1st movement and the LA dives at 12kts from snorkling depth to intermeadiate 1. T56 continues at 13kts. Range between ships is 2.6nm. What about the torpedo? Its at 2.4nm and closing. The to hit roll doesnt occur until the T56 and torp "meet". Detection phase and the T56's chance to detect the torpedo (and hence take evasive action) is unchanged becase i cant see anywhere that a fired topredo changes the detection possibility (only affects passive chance). So 50% to detect sub (89 so no) and torpedo (44 - yes). T56 picks up the torpedo but cannot classify it. Given the speed (55kts) of the contact they could assume its a torpedo. 1:21:5 Sub continues at 12kts and drops to Intermeadiate IV depth. T56 having picked up the torpedo will do a 180 turn again and try to outrun/head for home, increasing speed to 32kts. LA Class now 4.5nm from T56. Torpedo closes to 0.5nm. LA Class detection roll 25+15% is a 2 so maintains detection. T56 chance to detect Sub is 0 since it is travelling at 32 kts and is effectively blind. 1:24:5 LA class plots to continue the chase and directs itself at the fleeing T56. Speed maintained at 12kts. T56 fleeing. Torpedo following and will catch up this turn. Movement happens and the torp catchs the T56 so lets work this out. Page 6-28 for homing torpedoes table and the T56 doesnt have any ACM, but the table only goes as low as 1st G. Am i missing something? I will use 1st Gen anyway so homeing torpedo has 75% chance to hit before being modified by TMA. 6.5.2.3 gives TMA mods to the attack. I assume the range is taken from when the torpedo was fired? So the math is 75% for 3rd Gen torpedo and 0.8 for a fair solution means to hit chance is 60% To hit roll is a 5. The T56 is hit. This is turning into a mega post and i already have a list of other things to cover, so i will move straight to damage on the T56. The Mk 48 torpedo does 75 damage points to the T56 which has a total of 101 before it sinks. The T56 is limited to 16kts due to lose of damage points. Critical hits 75/(101-75) = 2.88 or many many critical hits. Without extrapolating the table on page 7-2 lets say 10 crits. Flooding Eng'g Eng'g Flood Eng Sonar Flood Flood Sonar Rudder. Lets do the flooding first. 4 flooding rolls see's 2 minor, a major and a sever flooding result. Minor = 2% of points lost per 30 minutes. This is doubled for 2 results i guess. Major = 4% of points lost and speed reduced to 15kts. Sever = loose 6% damage points. Adding up the %s 6+4+2+2=14% so not quite the 15% necessary for a capsize result (7.3.2.7). Eng'g rolls. Speed reduced to 0kts and minor fire in enginearing compartment. Sonar out of order. Rudder damage. Thats a lot of damage. If left to fend for itself the T56 is going to have difficulty over the next 30 minutes just to stay afloat due to the extensive flooding. In my mind the LA class would turn on the T56 and sink her outright (newspaper reports mystery loss of T56 at sea). But for the sake of the game i want to see how long she will last if the LA Class moves off. 1:54:5 (or 30 minutes later) Extra damage points lost via flooding. 101 damage points of the T56 x 14% = 14 so damage points were 101 - 75 (torp) - 14 (flooding) = 12 left and in the next 30 minutes it will sink unless all flooding is contained. In any case, flooding points will be > 15% of total in the next 30 minutes and she will capsize. The T56 is toast and i finished up the engagement here. Things that have occurred to me in hindsight 1) It was good to go to periscope depth and use the visual sighting rules. 2) The LA Class could have operated better tactically by diving below the thermaline layer, moving faster, then coming back up to locate the ship. 3) Is this type of AAR too long? Is the turn-by-turn nature of it too dry? Or is referencing some of the rules useful even??? 4) Cavitation modifiers only affect passive sonar detections, not active. 5) 6.5.1 restrictions on torpedoes ... should log what torpedoes are loading in each tube. It may matter one day. I didnt do this. When the T56 did 180 degree turns i should have checked for speed/turning distance stuff. I didnt, i had it turn on a dime. My solo random homemade movement table. I wanted a way of plotting my own movements first without knowing what the opposition craft movements would be. So i came up with random table. I plot my own crafts movements first, then roll to see what opposition craft will do before playing out the results. Step 1 Roll D20 to determine starting speed 1 = D8kts 2-3 = 25+D12 kts 4-7= 20+D6kts 8-12= 8+D6kts 13-20 = 14+D6kts Step 2 There is a chance each turn that the craft will "change" its plot. 15% chance intermediate turn 6% chance in a tactical turn 2% chance per engagement turn. If there is a change, roll D8 for what has changed on the list below. 1 Clear baffles. Does a 180 degree turn. Will resume original course when a 1 is rolled on a D6. D6 rolled each 3 minutes. 2 All stop (starts again 1 in 6/3 min turns) 3 Direction change (D8 * 45 degrees) 4 Speed & depth change 5 Speed, depth and direction change 6 Surface (radio, visual check) - only applies to subs 7 If craft has a towed sonar out, it brings it back in (and if the towed array is in then it puts it out) 8 .... um i'm looking for another action that could take place I have a table to roll on for depths similar to the speed table. Anyway, using the info above you may be able to work out how the T56 behaved and why. In this case it provided a good scenario.
May 7, 200916 yr Hello everyone. Harpoon noob signing on here. Was in a European Navy once but never saw the deck of a ship. Anyway, just wanted to point out that 4.4.5.1.4 tells us that a ship going active with their sonar count as a Loud target. Hmm. Is it just me, or is the rule and its example contradicting each other about what frequency sonars can detect each other? Not listed as H4.1 errata, though. Depending on which is right, it might come into play here, getting the poor old shallow-water subhunter detected from even further away. A Primaguet DD with towed passive array deployed seems like a more fair match, 1976 vs 1979 instead of 1976 vs 1962 As for the ACM gen ... if you notice, the "Torp Ph" and "Evasive Manvr" columns don't change at all depending on ACM gen, only depending on torpedo seeker gen. So you did right, AFAICT.
May 7, 200916 yr Anyway, just wanted to point out that 4.4.5.1.4 tells us that a ship going active with their sonar count as a Loud target. Hmm. Is it just me, or is the rule and its example contradicting each other about what frequency sonars can detect each other? Not listed as H4.1 errata, though. Depending on which is right, it might come into play here, getting the poor old shallow-water subhunter detected from even further away. The rule states: "Active sonars are rated as Loud targets and are detectable by sonars with the same or the next lower frequency band". And, then the rule gives an example: "Thus, an MF sonar could detect MF and LF-MF transmissions but not HF and LF transmissions". I admit I was confused by this rule and the example myself until I realized (after it was explained to me) that LF-MF was itself a sonar frequency band. HF MF LF-MF LF VLF-LF So, an HF sonar, for example, can detect both HF and MF, while a sonar MF can detect both MF and LF-MF, and so on.
May 7, 200916 yr The rule states: "Active sonars are rated as Loud targets and are detectable by sonars with the same or the next lower frequency band". And, then the rule gives an example: "Thus, an MF sonar could detect MF and LF-MF transmissions but not HF and LF transmissions". I admit I was confused by this rule and the example myself until I realized (after it was explained to me) that LF-MF was itself a sonar frequency band. HF MF LF-MF LF VLF-LF So, an HF sonar, for example, can detect both HF and MF, while a sonar MF can detect both MF and LF-MF, and so on. Yes, the example is clear, but what the rule _says_ is that a MF active sonar _is detectable by_ MF and LF-MF passive sonars. Isn't it? "are detectable by sonars with the same or the next lower frequency band" Which contradicts the example. To be consistent, the example would need to read "Thus, an MF sonar could detect MF and HF transmissions but not LF-MF and LF transmissions". Or be changed to "a MF active sonar could be detected by MF and LF-MF passive sonars but not by HF or LF passive sonars"
May 7, 200916 yr Yes, the example is clear, but what the rule _says_ is that a MF active sonar _is detectable by_ MF and LF-MF passive sonars. Isn't it? "are detectable by sonars with the same or the next lower frequency band"Which contradicts the example. To be consistent, the example would need to read "Thus, an MF sonar could detect MF and HF transmissions but not LF-MF and LF transmissions". Or be changed to "a MF active sonar could be detected by MF and LF-MF passive sonars but not by HF or LF passive sonars" I see what you're saying. The rule talks about what is "detectable", while the example talks about what can be "detected". But isn't the end result the same? For example: An active MF sonar can be detected by other MF (same band) or LF-MF (next lower band) sonars; AND A passive MF sonar can detect active MF (same band) or LF-MF (next lower band) sonars.
May 7, 200916 yr I see what you're saying. The rule talks about what is "detectable", while the example talks about what can be "detected". But isn't the end result the same? For example: An active MF sonar can be detected by other MF (same band) or LF-MF (next lower band) sonars; AND A passive MF sonar can detect active MF (same band) or LF-MF (next lower band) sonars. No, since that's not equivalent statements. If we extend your example a bit: For example: An active HF sonar can be detected by other HF (same band) or MF (next lower band) sonars; AND An active MF sonar can be detected by other MF (same band) or LF-MF (next lower band) sonars; AND An active LF-MF sonar can be detected by other LF-MF (same band) or LF (next lower band) sonars; AND A passive MF sonar can detect active MF (same band) or LF-MF (next lower band) sonars. ... they don't match. The passive MF must detect the active HF, and not an active LF-MF. Right?
May 7, 200916 yr Curses, WOC! I thought I had this rule licked, now I'm more confused than ever. Going to have to think about this one, and seek guidance from the H4 gurus. Maybe I can get someone from the 'top brass' to explain it. Edit: Email sent along to those in the know. I will update the thread when I get an answer.
May 8, 200916 yr KC, I was looking over your example and I have a few comments. I'll post some comments about the sub tactics at the end of the post, but I wanted to start with the sonar range calculations. Before I get too far into this, I want to recommend that you go to the Admiralty Trilogy CIC at the Clash of Arms website and download the H4 Sonar Calculator Excel file (http://www.clashofarms.com/the-cic.html and look under Harpoon for the calculator). It seems like you are using the hull mounted sonars for both vessels, so I won't worry about towed arrays right now. For the calculations I'm assuming you are using a Sea State of 1 - 4 (so the modifier is x1). Also, you have the sub approaching at Intermediate I depth, which is considered below the layer, so all the detection attempts are cross-layer. For the T56 ASW DD, the DUBV 23/43 is a MF sonar with a base range of: Active 3.4 nm and Passive 1.3. Looking at the modifiers for sonar I see the following modifiers (Note: I only included those that are not x1): Active: Target has Anechoic coating (x.5), Target Cross-layer (x.5). The base 50% range calculation is 3.4x.5x.5 = 0.85 rounded to 0.9. So the detection ranges turn out to be: 75% = 0.4, 50% = 1.0, 25% = 1.4. If the sub is above the layer this changes to a base 50% range = 1.7 with detection ranges of 75% = 0.7, 50% = 1.9, 25% = 2.6. Passive: If the ship decides to use passive sonar, the modifiers are Target is VQuiet (x.5), Target Speed 20kts (x6), Own Speed 12kts (x.5), Target cross-layer (x.5). The base 50% range calculation is 1.3x.5x6x.5x.5 = 0.975 rounded to 1.0. So the detection ranges turn out to be: 75% = 0.4, 50% = 1.1, 25% = 1.5, which is slightly better than the active ranges. For the LA class SSN, the BQQ-5C/D is a LF-MF sonar with a base range of: Active 4.7nm and Passive 3.8nm. I'll only look at the passive modifiers for this example. Passive: Target is Noisy (x2) [Note: if the DD uses active sonar it is considered a Loud noise rating, which is x4. I will show the calculations for both an active and passive DD], Target Speed 12kts (x2) [Note: the DD is considered to be cavitating, so the final passive detection range is doubled], Own Speed 20kts (x.25), Target cross-layer (x.5). The base 50% range calculation vs. a passive DD is 3.8x2x2x.25x.5 = 1.9, doubled for cavitation to 3.8. So the detection ranges turn out to be: 75% = 1.5, 50% = 4.2, 25% = 5.7. If the DD is using active sonar, use the Loud noise modifier (x4); but you wouldn't apply the cavitation modifier, since the reason the DD is Loud is its active sonar. With those basic calculations from your example out of the way, I want to talk about a couple other things. First off let's look at towed arrays. If the sub is really chasing the DD, then it will be in the destroyer's baffles, making detection from the ship's hull array impossible. However, the French DUBV 23/43 is combined hull and towed (VDS) array, so deploying the VDS will still provide detection capability and it could be deployed below the layer to avoid the cross-layer modifier (Note: if the VDS is deployed below the layer, the base range for active is 1.7 and for passive is 2.0). For the sub; if you allow it to deploy the TB-16D towed array and make course changes to allow the towed array to be in detection arc, you get a longer detection range for the sub. TB-16D base range is 5.1 nm and the modifiers are Target is Noisy (x2), Target Speed 12kts (x2) [Note: the DD is considered to be cavitating, so the final passive detection range is doubled], Own Speed for high speed array 20kts (x.5), Target cross-layer (x.5). The base 50% range calculation vs. a passive DD is 5.1x2x2x.5x.5 = 5.1, doubled for cavitation to 10.2. So the detection ranges turn out to be: 75% = 4.1, 50% = 11.2, 25% = 15.3. It should also be noted that the TB-16D would not get the Loud target modifier if the DD is using active sonar since it has a VLF-LF frequency range. Next up, let's look at some tactics for the sub. Rather than driving directly toward the target (I'm assuming that sub already has an idea of where the target DD is) at high speed (20 kts), I would use a sort of sprint and drift type of tactic, where high speed is used while diving below the layer (speed could even go up to 24 kts without changing the passive detection modifiers) and a slow speed (8 kts for best detection, but up to 14 kts still gives a good detection range) above the layer used to find the target and for course corrections to intercept. A quick look at the detection ranges for the slower speeds shows: At 8 kts: BQQ-5C/D base 50% range = 30.4, detection ranges: 75% = 12.2, 50% = 33.4, 25% = 45.6 TB-16D base 50% range = 20.4, detection ranges: 75% = 8.2, 50% = 22.4, 25% = 30.6 At 14 kts: BQQ-5C/D base 50% range = 15.2, detection ranges: 75% = 6.1, 50% = 16.7, 25% = 22.8 TB-16D base 50% range = 20.4, detection ranges: 75% = 8.2, 50% = 22.4, 25% = 30.6 One thing about the report; submarine/ASW is a slow long term thing, so I think the longer reports are fine. If you want to shorten, just move from the starting point to the first detection point without writing out all the attempts. I hope that helps out and I really recommend getting the Excel file. Dave
May 10, 200916 yr Author Wow. Thanks for the replies. I'll try and get my thoughts out there in a day or two. Once i've had some time to go through stuff.
May 12, 200916 yr Author Correct - i assumed hull mounted arrays since both were "moving fast". Dammit! For some reason i had it in my head the layer was after intermeadiate depths, not before it. Thats a brain fade on my part. I missed the cavitating modifier. Yep, i see it now. If the sub is chasing a ship the sub is in the baffles and not detectable. Good call. You wrote "It should also be noted that the TB-16D would not get the Loud target modifier if the DD is using active sonar since it has a VLF-LF frequency range." - can you point me to a rule? Sprint and drift tactic - agreed. I made a comment near the end of the AAR that the sub could drop below the layer and sprint. But my mistake was in where the layer was. I plan to try this tactic. It seems a bit exciting because the sub is sprinting along (effectively in the dark) and comes up above the layer to "see" where it is in relation to the ship. Depending on ship speed and any direction changes, the result could be interesting. The reason i made the post longer, by including detection attempts, was because i thought it might enable readers to see who had how much of a chance and for how long before detection took place. I hopped it added to the encounter rather than made it longer for no reason. But i can see both sides of the argument to include it or not. yeah, i'll grab that excel file - i know where it is.
May 13, 200916 yr Okay, guys, Larry Bond says the example given in Rule 4.4.5.1.4 is wrong and should instead read as follows: "Thus, an active MF sonar could be detected by passive MF and LF-MF sonars but not HF or LF sets."
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