el cid again
Here I will omit comments on ahead throwing weapons and on smart torpedoes - both of which were in Allied service
and effective late in WWII - and confine myself to depth charges - which were the basic international ASW weapon
of the period.
The reason for this discussion is reports that ASW in later war AS ships (notably Etrofu and Tacoma class) is too powerful --
combined with some early test results indicating EARLY war escorts have a far too high chance of actually damaging a sub.
Never mind most ASW attacks are on false targets - and NONE are in AE - so the weapons always have a possibility of hitting
a real target. I mean the chance of a hit are vastly too high - when only 2 DC are dropped nominally (a most unlikely attack,
as we shall see). So I can see how late war escorts with big patterns might be lethal?
I was a US Navy Electronics Technician Radar. Before I studied ASW and sonar, I assumed (even read) that sonar is kind of
like "radar with sound waves." In the crudest sense, that is true. But there is a real difference in precision of target data.
First of all - with radar - range is precise - but bearing less so. The wavelength and antenna size mean bearing is always somewhat
fuzzy - sometimes very much so - and rarely (with range only radar) non esistant. With sonar - it is the other way around.
Bearing is far more precise than range. You can tell the direction a sound comes from within a few degrees. But the path the sound
takes can vary - or even be multiple - and the distance it travels is never actually a strait line - so measuring time and calling that range
is not a perfect model. Range is always to some extent less clear than bearing - even when you have it. And passive sonar (and
hydrophones - sort of primitive passive sonar) ONLY give you bearing - no range at all. This techinical fact has a big impact on
DC attack patterns. You head in the direction of the sound - which you know fairly close - and drop a long string of DC - in part because
you do not know that actual range.
But there is more. You cannot drop until you reach the point the target was at. THEN you have to wait for the DC to sink. DURING
that time, the sub will almost always maneuver - unless it cannot - trying to get to a point different than you measured it at when you were
solving your attack problem. For technical reasons, there is always a gap in time between detection and reaching the "datum" point - or
drop point for your DC. And then there is always more time for the DC to reach operational depth and go off. During both gaps the sub will
move - ideally side to side - because your pattern is a sort of retangle - narrow and long - and going to the side makes it easier to get clear of the pattern.
ASW is inherently complicated - so a simplified model must omit a range of special theories and practices. But in general, pre war and early war DC patterns were smaller than late war ones. To that end, inventories of DC and DC launchers increased - to permit the larger patterns. Something omitted here is a discussion of the depth setting - which was not always the same for every DC - but in later war cases - might be more than one. Early - only one setting was used. But - here - we will omit that altogehter.
A DC rack would drop at different times in the same attack - precisely because where the target is (or will be when DC get down there) is always unknown. These are blind attacks. So you drop more than once. Typically four times, possibly six or eight - per pattern - from your rack (or racks).
Throwers are to make the pattern wider. They throw to both sides (wether a Y gun or two K guns in pairs matters not - you throw both ways - again because you do not know where the target will be - and it is a blind attack). This typically means a pattern ends up with three rows of DC - those from the rack(s) - and those from throwers to port - and those from throwers to starboard. In a long rectangle, centered on the target datum bearing when last taken - with the long axis being the range one - because that is less certain.
For this reason, the basic model "weapons on bearing times numbers" does not work well for ASW. You are firing in more or less all directions. But more than that, to avoid damaging the ship, and to let the DC reach depth - the attack ALWAYS ends up astern of the ASW vessel. So in that sense - the only direction is "stern" - and by the time they go off - you have no idea wether the sub stayed in place, speeded up, slowed down, moved to port or to starboard? It is very much a statistical thing - because the actual target movement must be unknown - the chances it went right or left are equal. [To that add it might have gone deep, gone to the bottom, or even gone shallow - something ignored here]
If an escort has 4 Y guns (or 4 k guns on each side) a standard mid war pattern might be 12 - 4 from racks - 4 on each side. If it has 6 - it might be 18. If 8 - 24. Patterns even larger were in use - and by both sides - in 1945 - but it is probably better to let AI do that as two attacks of 24 (or of 18) rather than force fewer shots every time - letting rolls simulate commander discretion.
By using such patterns - we can reduce the number of shots on the escort to a managable level. And make the pk per DC realistic. This is less than 1% - but if a pattern of 4 is used - 1% is close to right for small DC - and perhaps 2% for large ones. There is a special case - huge fast sinking DC almonst never used by RN in 1945 - they were LIKELY to hurt the DD - and they came from TT. They are not in the game - but if we put them in - we might use 3% per pattern of 4. However, as pattern size increases, the pk only goes up as the square root of number. Thus - a pattern of 9 (if somehow we had a ship with 3 throwers on a side plus a rack aft) would be just over twice the pk of a pattern of 4. Thus vastly larger patterns only have single digit pks per shot - putting ASW back in the right range - no matter the number of DC throwers on the escort. At the same time, the number of shots is not huge - so the escorts will run out if they engage in many attacks over a long voyage. A ship with 120 DC firing patterns of 24 gets 5 shots, for example. An early war DD with 12 DC off racks only gets 3 shots of 4.
< Message edited by el cid again -- 9/10/2011 4:43:18 PM >