@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.
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