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ASW Tactics

ASW tactics of a single DD

Escaping a single DD is fairly simple. However, it's always good to know what's going on on the surface. After the DD becomes alerted by an exploding torpedo or something else it starts pinging around at a speed of 5-7 knots. Usually the DD sets course to the point from where the torpedoes were fired or to the side of the target where the torpedo exploded.

If you are lucky and the DD doesn't get active sonar contact on you the DD will start to patrol in a circle with a diameter of 500-600 yards around the spot where the torpedoes were fired. But if the DD gains active sonar contact on you it will speed up to 14 knots and hunt for you.

I noticed that when the DD comes to a range between 200-100 yards to the sub the DD is able to locate the position of the sub EXACTLY and it changes its course towards the sub. It seems they can hear the sub-screws within this 100 yards. Only setting "All Stop" or "Silent Running" keeps the DD guessing where you are.

After the DD drops its first DCs on the sub it will slow down to 7-5 knots and follow the last known course of your sub. (If the last "contact" ping was when you were on course 256dT the DD will change its course to 256dT.) I watched this behavior in 90% of all tests.

The deaf spot

So if you can manage to escape to the other direction you should be behind the DD where it is "deaf" and you can speed up to 2/3 without them hearing you (once I set "all flank ahead" and they didn't notice me). The DD doesn't even ping in this direction.

IMPORTANT! Please note that from this point on you have to click on the thumbnails for full-size images.

The DD will keep this course for about 1500-1800 yards and start circling at 5 knots now. Once again with a 500-600 yard diameter. If you were fast enough you should be out of "active sonar range" now and the DD lost almost every chance to regain contact on you.

Behavior of one DD

After some circles the DD follows
the scattered convoy.

After some circles (4-7) the DD speeds up to 24-30 knots and follows the scattered convoy. So keep an eye on the heavy screws on the chart and try to get away from the track the DD will take to follow the ships or the active sonar contact may be regained to the sub.

There's one more behavior I watched in the test. If there is only 1 ship in the convoy with a single DD acting as escort and this ship gets sunk the DD starts pinging but speeds up to maximum speed and heads away as fast as possible without looking for the sub. But if the DD gets an "active sonar contact" it will slow down and start ASW. (In fact I had to add a second merchant to the convoy because in 4 of 5 tests the DD was unwilling to attack me.) If the DD gains a "contact" ping on the sub the following attack will be halfhearted too but the same tactic is used. It will travel 1500-1800 yards along your last known course and start to circle, but only 1-3 times. Then the DD will head away at max. speed.

ASW tactics of 2 DDs

Surviving against 2 DDs is a lot harder than against a single DD.

If there are 2 DDs protecting a convoy, they are using a completely different strategy than only one DD would use.

After the escorts became alerted they immediately begin pinging around and decrease their speed to 5-7 knots. Surprisingly they often don't change their course. But as soon as only one DD gains active sonar contact both DDs will turn around and head down to the sub's position at 14-16 knots. At this point the escorts don't show clear tactics for the rest of the attack run. Both DDs will run over the last detection point and drop some DCs.

While a single DD would follow the last known sub course, the 2 DDs show another tactic in every single attack run. Sometimes they turn around after only 400-600 yards and deliver DCs again. Another tactic is after they set off the DCs they make a little turn (20-45d) slow down to 5-9 knots and move on in this direction for 1400-1700 yards, finally circling some time at this position. Usually the distance between 2 circling DDs is 2000 - 2500 yards. But they will NEVER follow the last known sub course like a single one.

The "deaf" spot, the area behind the DD where nothing can be heard seems to not exist with 2 DDs even if both of them are heading in the same direction. A sub moving at 2/3 ahead can still be heard by the DDs at a distance of 2300 yards or more. So never speed up more than 1/3.

The DDs don't show real teamwork. There are only 2 scenes when they seem to work together:

1. If one DD detects sub screws or gains active sonar contact the second DD will be informed and head down to the location.

2. When no active sonar contact or sub screws can be detected the 2 DDs never circle in the same area.

ASW tactics of 3 DDs

Three DDs

Chain of 3 DDs (just speeding up and
turning around after I ordered 2/3 ahead)

3 DDs in general act like 2 DDs when they are hunting a sub.

After alerted by a torpedo they immediately turn around and hunt down to the wounded or destroyed merchant. With 3 "eyes" watching around they will surely gain active sonar contact soon. The angles to the sub are too different to minimize the sub's profile to the DDs most of the time.

If all DDs are hunting down to the sub from the same side they will deliver their DCs and then join up to provide scanning of the same area. They often build search-chains or triangles with a distance of 1000 - 1500 yards between the DDs.

If the DDs don't come in from the same direction each DD will deliver his DCs and then head on in the same direction with a little course change of 15-20d just after the DCs were dropped.

Three DDs

Triangle of 3 DDs (alerted by the
loud sub screws once again)

After the DDs passed and the DCs exploded the DDs act similar to 2 DDs. They show no special teamwork and vary their tactics with every single DC run. Sometimes they turn around immediately after the DCs exploded, sometimes they keep their course for 2000-2500 yards.

Really unpredictable.

After the DDs lost the contact to the sub for a while they build a triangle or a chain and circle. When they can't regain contact to the sub the DDs leave the area to meet the scattered convoy.

Special ASW tactics

Special tactics

DD drops a second pattern
of DCs after only 50-100 yards

During the many tests I was running I noticed some really strange tactics DDs sometimes use.

First I always thought when a DD drops DCs he will drop them and then run on, turn around and run a new attack. But sometimes DDs drop 2 loads of DCs in the same attack.

The second strange tactic I watched was DDs turning off their engines.

Sometimes I wondered why the DDs' screws disappeared even when they were closer (500 yards). This especially happened when they were very close and had no active sonar contact and the sub's engines were turned off. Once I had marked a DD and watched its details on the TDC. Its sound disappeared and it rapidly lost speed. It seems when they have no idea where the sub is they turn off the engines to detect the sub's screws.

Sometimes a second DD stays near the "silent" one to cover the silence of the one with its own noise.

So if the screws of a near DD disappear at once immediately switch to "all stop" or you will be detected even if you're at "silent running."

(Some months ago I was sunk by an "invisible" DD while I was sneaking away from 3 others and switched to 1/3 ahead exactly under the "silent" one when I thought I had enough distance to the 3 others to risk some noise.)

DCs were dropped no matter what's near the explosions. Sometimes DDs move into the explosions of DCs which were dropped from the DD ahead. They also are able to move "through" ships. Sometimes 2 DDs cross each others' way and seem to collide but they move on without any damage. Must be a program failure.

I also discovered a big problem DDs seem to have during ASW.

In 90% of all attack runs the DD lost active sonar contact when the distance was less than 500 yards to the sub, even when he "saw" the sub's full profile. But the DDs reacted on every course change I made after the DD lost contact and the DCs were delivered really close to the sub. These DD crews seemed too be able to detect the sub's screws even at "silent running" at a distance of 200 - 300 yards.

Escape tactics

Escaping a single or 2 DDs is not too difficult for most skippers even if the DDs have elite crews on board. It's a lot harder to survive ASW from 3 and more DDs, and the one and only save way to survive it is a well positioned thermal layer. But during the tests I discovered a good tactic to minimize the risk of being damaged by DCs during the ASW (based on the sonar problems I mentioned above).

Special tactic

1: flank speed, 15d right rudder; 2: all stop, full left rudder.
The DDs followed the last known course (black line)
and dropped the DCs at the wrong place.

After a DD gains active sonar contact he will hunt for the sub. When he comes closer than 1000 - 1200 yards (the screws can be heard) I went to flank speed (they already know where I am and it doesn't matter when the screws give away my position) and I try to turn around the sub to a heading + or - 10d to the DDs relative bearing to move almost the same way the DD does (the DD has to be AFT). After that I decrease my rudder to 5 or 10 to let the DD know I'm circling around. As soon as the DD comes closer (500 yards) the active sonar contact will be lost and the crew up there only knows where I am because I'm very loud. Now I switch to "All Stop" to play "dead man in the water" and change to full rudder (35) to the other direction. The speed I reached due to the "Flank ahead" will help to change my course very rapidly. The DD will follow my old track when I was at a rudder of 5 or 10 in the other direction and the DCs will splash down 200-300 yards away from me. After the DCs hit the water a short "Flank ahead" sprint gives enough speed to drift away at "1/3 ahead" after the DCs exploded. If there are more DDs with active sonar contact on the sub they should have lost it now and drop the DCs around the first ones. But if there's one more DD with active sonar contact I simply repeat this tactic. During the tests my boat was never damaged when I used this tactic even when the sub was at only 150 feet depth.

At a depth of 350 feet and 100% realism my boat wasn't even damaged when the DCs were dropped exactly over the boat.


All tests were made in Dec. 1944.

Every DD had an elite crew. Realism would have been 100% but I had to uncheck "Realistic Charts" to observe the DDs. I used a Gato-class sub with elite crew.


Don't rely on these tactics during the game. Individual escorts may act differently depending on experience or date.

Copyright © 2002 by Eric Hrogard. All rights reserved. Used with the author's permission.