"U-Boot am Atlantik" /Periscope 'rangefinding'

Discussions on the equipment used by the Axis forces, apart from the things covered in the other sections. Hosted by Juha Tompuri
Der Maresal
Posts: 24
Joined: 29 Aug 2002 21:33
Location: Bucarest, Dacia

"U-Boot am Atlantik" /Periscope 'rangefinding'

Post by Der Maresal » 07 Nov 2002 20:40

How does the U-Boot commander estime speed and distance to target using the persicope?

The gradual markings- horizontally, and vertically - correpond to the arcs of degree from what I know - The full mark represent full degrees, while the smaller ones in between are fractional markings.

From what I know the Commander must know the Target Ship and stimate the Mast height, and then there is a formula - TAN something "/" over something - and that's how he finds the distance -

But how does he find speed of Target, let's say a convoy of ships moving 4 to 8 knots - or a destroyer approaching fast?

I have some knowledge about this - but I'd like to hear it from some Experts on Submarine Warfare.

*I guess you must have been very good in Geometry and Mathematics, have a good eye sight - not anybody could become 'U-Boot Kommandant'
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Posts: 85
Joined: 29 Nov 2002 12:04
Location: Waiting in ambush beneath the waves...

Post by U99 » 30 Nov 2002 12:49

I'm hardly an expert on anything, but seeing this is quite an old topic and no one's answered it, can I have a go?

I've always heard range was calculated by taking the percieved height of a ship from the waterline to the top of the mast, then the range was figured out using a sliding scale.

AFAIK, speed wasn't figured out with the periscope. It was calculated by the use of the listening apparatus to count propellor revolutions. This was used to plot the movement of the target ship in relation to the movement of the submarine. Then both the range and speed were fed into calculating machines and an aim-off was provided in the form of a DA for the British and Japs, or a torpedo course setting for the Germans and Americans.

Of course, there was a lot of skill involved with these judgements, as you say. Rough seas might make this a bit tough, and it would be harder with destroyers closing in on you. Most often the range was exaggerated. Targets might move in an erratic zig-zag fashion, and air and sea escorts made for even quicker neccessary calculations made, firing, then a deep dive and escape. Torpedoes were shot by German CO's usually in pairs, because a full salvo fired from all tubes is such a loss of weight as to possibly upset the trim.

The British CO's were a lot more blase about this procedure than their German counterparts. John Stevens once remarked "I say if a target is worth firing at, give him the lot and, anyway, the DA is always ten degrees".

I agree not everyone could become U-boot Kommandant. But I think the aggressiveness, determination, patience, coolness under pressure and following good training was a bit more important than geometry and mathematics. And the respect of your crew was the most important.

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