SUBSIM Radio Room Forums - View Single Post - Oxygen in U-boat - U-boat Officer's Reply

Stiebler · 08-19-11, 07:38 AM

@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.

08-19-11, 07:38 AM	#3
Stiebler Fuel Supplier Join Date: Oct 2005 Location: London, UK Posts: 1,237 Downloads: 29 Uploads: 4	@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. __________________ NYGM Tonnage War Mod - More than a mod: it's an experience!