Tips for Type-XXI

[Gustav Schiebert]

Hi guys - so, after six patrols starting in 1942, Oblt z. See Ernst Heller has taken the Type IX boat U-156 and sunk 230,000 tonnes of enemy shipping. It's now May 1944 and I've sucessfully applied for a transfer to 11th Flotilla in Bergen, and given command of U-2540, one of the latest Type XXIs.

Does anyone have any experience or hints/tips for getting the most out of this boat? Specifically:

Although it's much faster underwater, how vulnerable is it to active sonar?
Not sure quite how the 'silent speed' works - pressing 'Z' gives me a speed of 7kts, seems a bit fast? Is this wonder weapon really that good?
What are people's experiences with safe distances from escorts - for example, even at silent speed in my Type IX I normally start diving once within about 1000m of a destroyer. Can I get closer in an XXI?
How stealthy is it (in regards to active sonar) while running diesels underwater, ie with the schnorkel up?
With its super underwater speed, is running away at top speed (rather than silent - ie slow - and deep) a viable tactic? Although destroyers are faster they can't use asdic when travelling above about 12-15kts, and I can go 17 underwater.
Basically, as I don't have my stealth meter I can't tell weather I'm being over-cautious or over-loud in my attacks. I'm not generally being detected, so I suspect it's the former, but if anyone has any thoughts on which engine settings/speeds are best I'd love to hear them.

Have done a search for 'Type XXI tips/guide' so sorry if this doubles up a previous post. Thanks guys!

[Hinrich Schwab]

Hi guys - so, after six patrols starting in 1942, Oblt z. See Ernst Heller has taken the Type IX boat U-156 and sunk 230,000 tonnes of enemy shipping. It's now May 1944 and I've sucessfully applied for a transfer to 11th Flotilla in Bergen, and given command of U-2540, one of the latest Type XXIs.

Does anyone have any experience or hints/tips for getting the most out of this boat? Specifically:

Although it's much faster underwater, how vulnerable is it to active sonar?
Not sure quite how the 'silent speed' works - pressing 'Z' gives me a speed of 7kts, seems a bit fast? Is this wonder weapon really that good?
What are people's experiences with safe distances from escorts - for example, even at silent speed in my Type IX I normally start diving once within about 1000m of a destroyer. Can I get closer in an XXI?
How stealthy is it (in regards to active sonar) while running diesels underwater, ie with the schnorkel up?
With its super underwater speed, is running away at top speed (rather than silent - ie slow - and deep) a viable tactic? Although destroyers are faster they can't use asdic when travelling above about 12-15kts, and I can go 17 underwater.
Basically, as I don't have my stealth meter I can't tell weather I'm being over-cautious or over-loud in my attacks. I'm not generally being detected, so I suspect it's the former, but if anyone has any thoughts on which engine settings/speeds are best I'd love to hear them.

Have done a search for 'Type XXI tips/guide' so sorry if this doubles up a previous post. Thanks guys!

The war was all but over by the time the XXI became active, so most of its battle performance is still conjecture. In game, the tactics for destroyer evasion remain unchanged except for the following:

1. Submerged speed. While you can run past the washout speed of detection gear, it is best to do this only to escape a search pattern AFTER dropping a BOLD 3 or better to distract the destroyer.

2. Silent performance. While the XXI is quieter and can run slightly faster and remain quiet, don't push your luck.

3. True Crush Depth. This is where the XXI shines a bit. Its hull is strong enough to allow you to get deep enough to confuse or evade late war sonar, which WILL bust the older boats.

In short, you have just enough new advantages to survive the late war. None are a guarantee, but you have a fighting chance whereas the II, VII and IX boats have next to none against late-war ASW.

[Gustav Schiebert]

@Hinrich - thanks for those, I printed them out and had them to hand on my first patrol, very handy!

Definitely agree about the speed vs depth thing. I did some experimenting and found that if you do try to outrun a destroyer he can just pick you up with active sonar instead and increases his speed. Silent and deep as you say seems to work well. In terms of speed i think it's just like the old days in a Type VII, no faster than 2/5. The extra 10 kts just gives you more leeway in getting into a good position.

Anyway, first patrol - 2 destroyers and a large tanker. Not loads, but enough!

[Hinrich Schwab]

@Hinrich - thanks for those, I printed them out and had them to hand on my first patrol, very handy!

I did some experimenting and found that if you do try to outrun a destroyer he can just pick you up with active sonar instead and increases his speed.

I do not know what you were trying to do, but DDs have a max speed starting at 35kts and DEs around 25kts. No sub can outrun a destroyer or destroyer-escort. Congrats on your late war kills:up:

[Marcello]

How stealthy is it (in regards to active sonar) while running diesels underwater, ie with the schnorkel up?Planes seem to be able to detect you quite well when snorting, even if you are conservative about it, though I am patrolling busy areas so it might be just my impression. In fact as long as I limit myself to attack isolated merchants and steer clear of warships the only real threat is from aircrafts, either by being bombed in Bergen right out of the dock or by being detected and attacked when snorting. In particular if you stick to realistic harbor speeds there is a very good chance of being on the receiving end of an air raid before you can clear the target area.
That said if surface escorts do find you Hedgehog is a nasty thing to be on the receiving end of. Running can help here, but of course you cannot just run as already said.
I have never dared to use snorkel anywhere close to a warship but only to recharge batteries, renew air supply and in some particular conditions (poor visibility but calm sea and still not in hot areas)..

[Gustav Schiebert]

I do not know what you were trying to do, but DDs have a max speed starting at 35kts and DEs around 25kts. No sub can outrun a destroyer or destroyer-escort. Congrats on your late war kills:up:

Ah yes, not straight outrunning but just so they can't ASDIC me - or is that a waste of time?

And Marcello, thanks for those words they're very helpful. Is there a shortcut key for the schnorkel? I know : does schnorkel depth, but it's a bit annoying to have to keep speaking to the LI every time I want to have a peep through the 'scope.

[Marcello]

To raise and lower the snorkel there is the X key.
My procedure for snorkel is as follow
1) Press P to go to periscope depth
2) Raise attack periscope (Ctrl + Up) and give a look around, at least one scan at sea level for ship and one at the sky for aircrafts (for what little is worth...).
3) Raise snorkel (X) and observation periscope.
4) Lower attack periscope
6) Cross fingers

Generally I snort 2-3 times a day. One time around midday to renew air supply, generally 10-15 minutes and no more. Then a couple of hours during the night to recharge batteries, generally an hour around midnight and another hour before dawn. I am very conservative with batteries charge and bottled oxygen supply (I use Hsie patch).
I have been advised to keep TC low (say 8x or less) during snorting and that is indeed a very good idea, double so during the day I might add. I have also been told that crew might pick up aircrafts (personally I have never managed when running the periscope watch by myself) via the observation periscope, however in truth so far I have relied on the noise meter as ersatz RWR until the proper snorkel mounted unit becomes available. I doubt I would have survived a single trip to AM52 without either; even so I usually keep the fingers permanently on the X and crash dive button while snorting with any TC.

Biggest problem you cannot solve by changing destination or tactics IMHO is Bergen. If you stick to semi realistic procedures, say one-two knots to leave the bunker, max 5 knots within the harbor and following the minesweeper you are still going to be near the town when the B-17s or whatever show up and that happens quite often. Afterwards it is fireworks time and you will be in the middle of it; I must have aborted about one third of the patrols after having taken some damage from them.

So far I have not engaged many convoys in the career mode but from what I have seen the best option seems to be firing a salvo of pattern runner wet-heater from standoff range at night and trying to slip away after that. In the event there are enough single ships to achieve decent tonnage where I usually go. Taking a breath however gets risky...

[Gustav Schiebert]

Thanks for the tips Marcello - I've played SH3 for a while now but never done schnorkelling. That reply is getting printed out and put on my SH3 board next to the computer.

I've managed to sink a few ships, but nothing bigger than a small merchant in convoy.

Bergen is annoying, although it's fun to have a pop at the bombers. I admit sometimes I break the speed limit when coming out of port, when the bombs are falling around me.

[Randomizer]

More on snorkelling here:

Snorkel detection by airborne radar etc. (http://www.subsim.com/radioroom/showthread.php?t=200866)

[Marcello]

Some additional thoughts.
In transit I mostly travel underwater at a speed of 3 knots, sometimes increased to 4-5 at night between the two snorkel charges. I guess that if you are more comfortable than me with a greater battery drain and longer recharge time cruising at 4-5 all the time could be an option. To compensate somewhat for this slow speed I sometimes run on the surface in bad weather, diving periodically to perform sound checks. Occasionally with fog but calm sea I have kept using the snorkel even after having topped the battery but this is a less frequent condition.
In patrol I stay almost always underwater running at 1-2 knots, except for attacks and putting some distance from my last sinking for which I increase speed as necessary.
Some additional suggestions from real life can also be found here:

http://www.uboatarchive.net/BDUOrder1.htm

[scramasax]

How can I reduce speed below 7 knots in XXI?

[Gerald]

Click on the meter for speed and make a manual adjustment of knots,and welcome to SubSim, Scramasax :sunny:

[AndreasT]

Well I was anaughty boy and added the mod for the XXI from 1939, cheating can be fun if one keeps tit to oneself.
Anyway, the XXI is just amazing at diving at speed. What bothers me is that at depth (250m) if I move at slow speed the boat sinks deeper and deeper.
Is this normal, do the other boats do this as well? I don't remember.
I always have to go up to 1/3 speed otherwise I will die deep.
The XXI is large so in real life I am sure it could be seen quicker by the enemy.
What I really dislike about the boat is that it drifts a long, long way after stopping. Which is a pain if lining up for a shot.
Visting harbours underwater is rather difficult now.
Otherwise I love the thing.

[Hinrich Schwab]

Well I was anaughty boy and added the mod for the XXI from 1939, cheating can be fun if one keeps tit to oneself.
Anyway, the XXI is just amazing at diving at speed. What bothers me is that at depth (250m) if I move at slow speed the boat sinks deeper and deeper.
Is this normal, do the other boats do this as well?

It is a combination of real life hydrodynamics and holes in the game engine. At deeper depths, depth keeping is a problem because of both increased external pressure and internal pressure changes with air volume due to Boyle's Law. However, a peak crew and expert manual trimming can minimize this or restore neutral buoyancy. It isn't easy, but possible. The game, however, uses crew abilities to determine trim keeping. At the lower depths, trim will not hold without speed to put the dive planes to work to keep trim. This works well in real life as the higher speeds are not an issue as cavitation occurs at much higher speeds at deeper depths because of pressure. Realistically, the XXI should be able to go fast enough to maintain trim, but remain relatively silent due to lack of cavitation and any thermoclines it may be underneath. At deep submergence (>220m) it takes ~5-7 knots to maintain trim. However, because of the simplistic noise propagation model, your odds of detection are not necessarily realistic.

[Gustav Schiebert]

How can I reduce speed below 7 knots in XXI?

Welcome aboard also!

And Schwab, thanks for that bit of info, I didn't realise that crew experience made a difference. I just took it as an extra little challenge, a taste of what it's like to be a Chief Engineer and manually trim 700 tonnes of U-Boat!

[Gustav Schiebert]

[QUOTE=Marcello;1994075]I have also been told that crew might pick up aircrafts (personally I have never managed when running the periscope watch by myself) via the observation periscope...
QUOTE]

Sorry for the double post but Marcello, I take it from that that if you run with the 'scope up the watch crew automatically do a periscope watch? Which crewman performs the duty, just so I can but my best man on it.

[Marcello]

[QUOTE=Marcello;1994075]I have also been told that crew might pick up aircrafts (personally I have never managed when running the periscope watch by myself) via the observation periscope...
QUOTE]

Sorry for the double post but Marcello, I take it from that that if you run with the 'scope up the watch crew automatically do a periscope watch? Which crewman performs the duty, just so I can but my best man on it.

Frankly I do not know, I have just been told here in the forums. On occasion when the noise meter turned red I tried to look for planes on the observation periscope instead of ordering an immediate crash dive, but without much luck so far.Even with the wide field periscope it would be easy to miss the plane until too late. Maybe if I had looked at the map instead I would have seen the triangles for aircrafts as told. But it is not something I feel like experimenting in a campaign.

It is a combination of real life hydrodynamics and holes in the game engine. At deeper depths, depth keeping is a problem because of both increased external pressure and internal pressure changes with air volume due to Boyle's Law. However, a peak crew and expert manual trimming can minimize this or restore neutral buoyancy. It isn't easy, but possible.My understanding is that once underwater submarines usually trim for slight positive buoyancy and use speed to keep themselves down rather than trimming for negative and holding themselves up dynamically. The safety implications of the latter in case of accident are self evident, but I suppose that there might be exceptions, I will try to look into this.
It should not be exceedingly complicated to trim accurately enough for such task. What I would suspect would be more difficult is depth keeping with a stationary boat, as the compensation by pumping would have to be much more frequent.

[Hinrich Schwab]

My understanding is that once underwater submarines usually trim for slight positive buoyancy and use speed to keep themselves down rather than trimming for negative and holding themselves up dynamically. The safety implications of the latter in case of accident are self evident, but I suppose that there might be exceptions, I will try to look into this.

Let me know what you find and its source. Regardless of the actual procedures, the issue is that the game does not take alternative procedures into account and the boat starts sinking at a certain depth without sufficient speed.