Oxygen in U-boat - U-boat Officer's Reply

[Stiebler]

Thanks for this feedback, and especially to Hitman for improvement/clarification of my translation.

I've mentioned in H.sie's sticky thread, that my U-boat friend is an intelligent man, who would certainly have volunteered information about use of compressed oxygen, if he knew of it (or, perhaps, if he remembered it).

Stiebler.

[Stiebler]

I wrote again to my friendly and helpful U-boat officer (let us name him: Guenther Paas), asking specifically about the use of compressed oxygen in U-boats. Again, for reference purposes in future encylopaedias, I attach his reply in its original German, and underneath my very literal translation.

His reply:
"Es ist richtig, dass die Unterseeboote neben den Druckluftflaschen auch Flaschen mit reinen Sauerstoff an Bord hatten. Beide Flaschenarten hatten einen Druck von 20 atü = bar. Die Druckluftflaschen wurden zum Anblasen bei Auftauchen verwendet. Die Flaschen mit reinem Sauerstoff wurden benötigt, wenn das Boot längere Zeit unter Wasser war und der Sauerstoff im Boot zu Ende ging. Wie ich Dir bereits berichtet habe, wird die durch das Atmen der Besatzungsmitglieder verbrauchte Luft, durch Kali-Patronen, die sich an der inneren Bordwand befanden gesaugt. Die Kali-patronen halten das Kohlendioxyd zurück und die sauerstoffarme Luft kommt zurück ins Innere des Bootes. Wenn der Sauerstoff in der Luft durch längere Unterwasserfahrt immer weniger wurde und die Besatzungsmitlieder anfingen zu "japsen" und nach Luft zu schnappen, wurde aus den Sauerstoffflaschen Sauerstoff abgelassen und man konnte wieder normal atmen.

"Trotz Rückfragen bei Horst Bredow und alten U-Bootsfahrern konnte mir keiner sagen, wieviel Druckluftflaschen und wieviel Sauerstoffflaschen die Boote an Bord hatten. Daher weiss ich auch nicht, wie lange die Sauerstoffvorräte ausreichten. Aus meiner eigenen Erfahrung kann ich sagen, dass bei längerer Unterwasserfahrt die Batterien leer wurden und wir auftauchen mussten. Dass der Sauerstoff aus den Flaschen zu Ende ging, habe ich nicht erlebt."

My translation is this:

"It is correct that on board the submarines, besides the compressed air-bottles, had also bottles with pure oxygen. Both bottle-types had a pressure of 20 atmospheres = Bar. The compressed air-bottles were used for blowing when surfacing. The bottles with pure oxygen were required if the boat was an extended time under water and the oxygen in the boat came to an end. As I have already reported to you, the air spent through the breath of the crewmembers is absorbed through potash-cartridges, that were positioned on the inner hull. The potash-cartridges keep back the carbon-dioxide and the oxygen-poor air comes back into the inside of the boat. If the oxygen in the air became progressively less, through over-long underwater-patrol and the crewmembers started to "japsen" and to snatch after air, oxygen was released from the oxygen-bottles and they could breathe normally again.

"Despite queries, at Horst Bredow [owner of the well known U-boat Archive] and old U-boat sailors, no one could tell me how many compressed air-bottles and how many oxygen-bottles the boats had on board. Therefore I do not know also for how long the oxygen-supplies were enough. From my own experience I can say, that the batteries became empty with extended underwater-patrol and we had to surface. That the oxygen from the bottles came to an end, I have not experienced."

In summary, no one now knows, but exhaustion of the U-boat batteries was the determining factor in when to surface.

Stiebler.

[U-Falke]

Great topic! May I ask a question?

Bateries were a vital resource.
Why in SH3 we can recharge them in 6 hours
while at SH5 it takes almost 12h?
I will not mention SH4, in wich you deplete a
XXI´ batteries cruising at 2 Knt, in a smaller time than
a type IIa in SH3 cruisng at the same speed...

[Hitman]

"Despite queries, at Horst Bredow [owner of the well known U-boat Archive] and old U-boat sailors, no one could tell me how many compressed air-bottles and how many oxygen-bottles the boats had on board. Therefore I do not know also for how long the oxygen-supplies were enough. From my own experience I can say, that the batteries became empty with extended underwater-patrol and we had to surface. That the oxygen from the bottles came to an end, I have not experienced."

Again very interesting and authentic reply To better put it into its proper historical frame, can we know in which period Mr. Paas served?

I suspect that early to mid war crews didn't suffer the limitations that late war crews suffered when it comes to endurance underwater. The logic says that if Mr. Paas is still alive, he will probably have served in late war, but knowing it can help us clarify better the whole thing.

[Stiebler]

@Hitman:

When did Lt Paas serve? Good question.
He was a midshipman aboard U-tanker U 461 in 1942 (one full war patrol to mid-Atlantic), then to officer training school, then appointed to a new VIIC U-boat in 1944. He participated in the usual six-month sea-training with the boat, including the tactical exercises against training convoys (and presumably including schnorchel training - I'm not sure about that), then was removed from the U-boat with serious illness. He was still in hospital at the end of the war, in 1945.
Clearly, Lt Paas would have received much experience with the daily details of running an attack U-boat during his intensive training period on his VIIC.

@U-Falke:
I do not know why the devs chose different recharging times for batteries in their different U-boat simulations. Possibly to make game-play more interesting for the casual player?

@Everyone:
Could we please keep this thread on-topic, for the benefit of any future researcher trying to discover authentic eye-witness information about U-boats? That is why I started this thread. Many thanks.

Stiebler.

[LGN1]

Thanks a lot for the information, Stiebler!

Do you know how long it took until they surfaced because of the batteries and at what speed they usually travelled submerged? From what I gathered elsewhere battery lifetimes varied a lot depending on age, speed (obviously),...

In addition, I don't think that they surfaced when the batteries were already almost empty. I guess they always wanted to keep some reserves in order to have enough power to escape in case of being attacked.

Regards, LGN1

[Stiebler]

@LGN1:

I can answer your questions immediately, with information previously obtained from Guenther Paas for a study that I did at his request on the sinking of U 461. (He was not aboard U 461 when it was sunk.) The original information about batteries came from Paas' chief engineer on the VIIC boat.

U-boat batteries could be charged in two ways:
1. Trickle (slow) charge. This was only practical at base, but gave a higher capacity to the battery when fully charged.
2. Fast charge by gearing from the diesel engines. This was used at sea. Fully charged was at lower capapcity (lower amps available) than from the slow charge.

U-boat commanders were always nervous about the state of their batteries, and surfaced to re-charge whenever safe to do so. However, it was not considered 'safe' in sea areas that were regularly patrolled by Allied aircraft, when the boats would surface only at night.

At certain times of the war, and particularly in the Bay of Biscay at two different times in mid 1943, orders were given by BdU explicity to remain submerged at all times, except to surface at night for the minimum time needed to recharge batteries.

As you have said, time for recharge depended on the depletion of their batteries and their state of repair. U-boats would proceed underwater for normal passage at 2 kts (sometimes a little slower, depending on battery capacity), when the batteries would last more than 24 hours. However, no sane commander would wish to exhaust the batteries, so all would try to recharge at least once per day.

Relevant to this topic, U 461 was sunk by air attack on the surface in the Bay of Biscay when its sister tanker U 462 was forced to surface prematurely during their underwater cruise as a result of defective batteries. (At least, that is one story, although it is more probable that both tankers and their U-escort actually surfaced in compliance with current standing orders: at that time to recharge batteries on the surface and to defend against air attacks with combined flak guns. But U 462 had been complaining of defective batteries of 2-3 months.)

Stiebler.

[Ligne Maginot]

Originally Posted by Stiebler

@Everyone:
Could we please keep this thread on-topic, for the benefit of any future researcher trying to discover authentic eye-witness information about U-boats? That is why I started this thread. Many thanks.
Stiebler.

I'm sorry, but it is a categorical imperative to keep it afloat (almost kantian meaning).

Best regards.

[JeromeHeretic]

Look at this movie:

They talk about high pressure and low pressure system. High pressure was used in big depth, low pressure system was used in small depths, but both systems was suplied from the same high pressure tanks, low pressure was created from high pressure by pressure dividing valve.

Yes, of course this movie is about US submarines, but in german it was principialy done in the same way. Maybe values of used pressure was a bit different.

[Sailor Steve]

[Obltn Strand]

Originally Posted by Stiebler

"It is correct that on board the submarines, besides the compressed air-bottles, had also bottles with pure oxygen. Both bottle-types had a pressure of 20 atmospheres = Bar. The compressed air-bottles were used for blowing when surfacing. The bottles with pure oxygen were required if the boat was an extended time under water and the oxygen in the boat came to an end.

20 atms of pressure air means a submarine can't blow it's ballast tanks in depths over 200m. Doing so results a backflow, as sea water rushes into air tank. One-way valve can prevent it but also air won't be transfered to ballast tank either.

Gas welding kit which uses mixture of acetylene/oxygen has oxygen pressure of 200 atms and it was around during ww2.

[SquareSteelBar]

Originally Posted by Obltn Strand

20 atms of pressure air means a submarine can't blow it's ballast tanks in depths over 200m...

Maybe a typo.
In his first post Stiebler wrote about 30 atm...

[LGN1]

Thanks again, Stiebler! Very interesting.

I've read again the first reply of Guenther Paas. He mentions that in most cases the batteries lasted only 18-20 hours with 'sparsamste Fahrt' (most economical speed?) and that at least after 12 hours oxygen/air had to be added (it's not clear whether air or oxygen is meant). I think, the current numbers in h.sie's mod are not too far off from this. Maybe the remaining difference is that at first compressed air was added not oxygen and that in many cases the Chief Engineer waited until the crew gasped for air (as G. Paas mentions in his second reply)

The numbers in h.sie's mod are based on the values given in the original VIIC handbook. There it's mentioned that the oxygen level should not drop below 17.5%. However, I can imagine that back then many commanders/chief engineers didn't care much about the number, but waited until the crew really suffered.

Has anyone access to patrol logs from the Norway campaign? I've read that during this campaign some crews had problems with their oxygen supply.

Regards, LGN1

[Stiebler]

@Oblt Strand, SSB:
Lt Paas says in his two different accounts:
30 atmospheres for compressed air.
20 atmospheres for compressed oxygen.

@LGN1:
It would appear from Paas' first account that his idea of 'sparsamste Fahrt' was faster than 2kts; probably 3 kts.
The concept of 'most economical speed' (to conserve power/fuel) is meaningless for batteries, since their nature ensures that 'the slower the speed, the much-longer they last'. If any vehicle can travel 100 miles at 10 km/hr on electric batteries, it will travel much further than 200 miles at 5 km/hr. That is the nature of battery discharge (assuming lead-acid batteries, as used in U-boats). Therefore sparsamste Fahrt must refer to 'most economical speed considering a) rate of progress; b) time before recharging'.

I forgot to mention battery charging times in my previous post.
Assuming batteries completely depleted:
Slow recharging at base took up to 24 hours.
Fast recharging at sea took 6-8 hours.
(Source: engineer on Paas's VIIC U-boat)

It would have taken U 462 five hours to recharge completely depleted batteries at 10 kts. Faster speeds would have caused faster recharging, but would also cause the batteries to over-heat, and this could not be attempted. (Source: F. Schmidt, maschinist, U 462)

Because of this long recharging time for a depleted battery, it was the custom to take every opportunity to recharge batteries when safe, as previously stated.

Schnorchel boats were a special case. Because they rarely returned to the surface, they had to schnorchel to recharge batteries and to refresh the air. War diaries show that normal practice was a 'short schnorchel' to refresh air, and a 'long schnorchel' to recharge batteries, both usually at night.

When you refer to the Norwegian campaign, when U-boats ran short on air, do you mean the campaign of 1940, or the schnorchel campaign of late 1944-1945 of boats based in Norway?

Stiebler.

[SquareSteelBar]

Originally Posted by Stiebler

@Oblt Strand, SSB:
Lt Paas says in his two different accounts:
30 atmospheres for compressed air.
20 atmospheres for compressed oxygen...

..."It is correct that on board the submarines, besides the compressed air-bottles, had also bottles with pure oxygen. Both bottle-types had a pressure of 20 atmospheres = Bar..."