Modifications and versions of the type T. Vh. Re. S3 calculator

The type T. Vh. Re. S3 torpedo calculator which entered the service in 1941, until the end of war remained the main component of German U-Boats fire control systems. However, in this period (1941-1945), on the basis of gathered experience, some improvements were done.

The early version of the device is described here and here. 

Wczesna wersja kalkulatora torpedowego T. Vh. Re. S3

Photo 1. The early version of the type T. Vh. Re. S3 torpedo calculator

 Wczesna wersja kalkulatora torpedowego T. Vh. Re. S3 w kiosku U 564 (połowa roku 1942)

Photo 2. The early version of the type T. Vh. Re. S3 torpedo calculator in U 564's conning tower (mid-1942) [1]

 Wczesna wersja kalkulatora torpedowego T. Vh. Re. S3 (połowa roku 1942)

Photo 3. The early version of the type T. Vh. Re. S3 torpedo calculator (mid-1942) [2]

 

The first significant improvement was an addition of the angle of impact switch and control lamp (Germ. Endlageschalter). This improvement is mentioned several times in the reports on the interrogations of survivors from sunken U-Boats.

 

Report on the interrogation of survivors from U 172 sunk 13 December 1943:

4.  After U-172’s fourth patrol, an angle-of-impact switch was built into the torpedo data computer. This was stated to help in the elimination of errors in firing. (For details of this switch, see Op-16-Z Final Report G/Serial 28 on U-841, page 24.) [3]

 

Report on the interrogation of survivors from U 177 sunk 6 February 1944:

Angle of Impact Switch
It was confirmed that the angle of impact switch is now a standard element of the torpedo data computer in U-boats. Installation of the switch was begun in December 1942. [4]

 

Report on the interrogation of survivors from U 575 sunk 13 March 1944:

T.D.C.  (Torpedo Data Computer)
Normal older type. Angle-of-impact switch built in at an undetermined time before the eighth patrol. [5]

 

Report on the interrogation of survivors from U 841 sunk 17 October 1943 and U 848 sunk 5 November 1943:

TORPEDO COMPUTER.
A coxswain stated that all boats have recently been equipped with a new torpedo computer (Vorhaltrechner) with an extra switch was not on the older type carried by the prisoner's previous boats. This is an angle impact switch (Endlagenschalter). The switch operates a light which goes on when the torpedo's hitting angle in side of ship would be greater than 90 degrees. The light goes on automatically when the relative position of the U-boat and the target is such that the above would result. When the light goes on, it gives warning that the calculations have ceased (they are automatically blocked off) the the data must be reset. [6]

 

The angle of impact control lamp was added to the front panel, on the left side, just below the drum showing the maximum distance the target.

 Płyta czołowa kalkulatora torpedowego z U 995 znajdująca się w muzeum w Laboe, z widoczną lampką kontrolną kąta uderzenia torpedy

Photo 4. The front panel of the torpedo calculator from U 995 with the angle of impact control lamp visible

Kalkulator torpedowy w kiosku U 995 z widoczną lampką kontrolną uderzenia torpedy

Photo 5. Torpedo calculator in the U 995's conning tower with the angle of impact control lamp visible [7]

Kalkulator torpedowy w kiosku U 505 z widoczną lampką kontrolną uderzenia torpedy

Photo 6. Torpedo calculator in the U 505's conning tower with the angle of impact control lamp visible [8]

 

From the reports quoted above and from the photographs dating, one can estimate, that introduction of the angle of impact switch and control lamp begun in the end of 1942. The purpose of this switch was to inform, that the torpedo impact angle was smaller than 30° or greater than 150° and thus eliminating the torpedo duds resulting from inadequate impact angle. The inadequate impact angle could result in improper operation of the impact exploder. The introduction of the angle of impact switch can be related with the introduction of the new impact-influence type Pi 2 exploder (first combat usage in December 1942). In the War Diary of the U-Boat Command (BdU KTB), on 10 May 1943, there are gathered the early experiences with the use of such exploders. Among the others, the operational limitation related with the necessity of keeping the impact angle in the range 30° - 150° was mentioned.

When the control lamp lit up, it meant that the torpedo would hit the target with too large (or too small) impact angle and the impact pistol could not properly initiate explosion. In such situation, the attack position should be altered so the impact angle became more favorable. 

 

The torpedo calculators on boards of type VIIC U-Boats were installed horizontally, while on the other types of the U-Boats vertically. This resulted in some construction differences: 

  • all dials and labels had to be adjusted accordingly to the orientation of the whole device;
  • into the torpedo calculator for type VIIC U-Boats the target follow-up switch (Germ. Blauschalter) was embedded, while on the other types of U-Boats, this switch was installed separately;

Kalkulator torpedowy przeznaczony dla U-Bootów typu VIIC (pozioma orientacja, z prawej strony widoczny zintegrowany przełącznik śledzenia celu)

Photo 7. Torpedo calculator for type VIIC U-Boats (horizontal orientation, the target follow-up switch embedded to the right)

Kalkulator torpedowy w kiosku U 505 (typ IXC) (orientacja pionowa, brak zintegrowanego przełącznika śledzenia celu, który jest widoczny jako oddzielny komponent z lewej strony kalkulatora)

Photo 8. Torpedo calculator in U 505's (type IXC U-Boat) conning tower (vertical orientation, the target follow-up switch is visible as separate element to the left of the calculator) [8]

 

  • the calculator for type VIIC U-Boats was fitted with the target bearing knob located at the front panel, in its right-top corner. In case of the calculators for other types of U-Boats, this knob was located at the right side;

Kalkulator torpedowy przeznaczony dla U-Bootów typu IXC z widocznym pokrętłem wprowadzania namiaru celu na prawej ściance, w jej dolnej części

Photo 9. Torpedo calculator for type IX U-Boats with the target bearing knob visible at the right side [9]

 

Most likely, this difference resulted from the final location of the calculator. In the conning towers of type VIIC U-Boats, the calculator was installed in such place, that its right-upper part was directly below the guide-bar for the attack periscope winch cables. If the knob had been located in that place, it would have been hard to operate, thus it was moved to the front panel;

Kalkulator torpedowy w kiosku U-Boota typu VIIC z widocznym pokrętłem wprowadzania namiaru celu na pokrywie czołowej (w górnej części zdjęcia widoczna jest wręga która utrudniałaby obsługę pokrętła, gdyby znajdowało się ono na górnej ściance)

Photo 10. Torpedo calculator in the conning tower of type VIIC U-Boat with target bearing knob visible at the front panel (in the upper part of photo a guide-bar is visible, which would make the operation of the knob difficult if located at the top side) [2]

Kalkulator torpedowy w kiosku U 995 z widocznym pokrętłem wprowadzania namiaru celu na pokrywie czołowej (zaznaczono także wręgę, która utrudniałaby obsługę pokrętła, gdyby znajdowało się ono na górnej ściance)

Photo 11. Torpedo calculator in U 995's conning tower with target bearing knob visible at the front panel (a guide-bar is also visible, which would make the operation of the knob difficult if located at the top side) [7]

 

  • the calculator for type VIIC U-Boats was fitted with two sockets at the front panel (in the top-left and the bottom-right corner) for connecting the drying gear (Germ. Trockengerät), while in case of the calculators for other types of U-Boats, these sockets were located at the right and the left side (in the bottom and the top part respectively);

Kalkulator torpedowy dla U-Bootów typu VIIC z widocznymi gniazdami przeznaczonymi do osuszania wnętrza na płycie czołowej

Photo 12. Torpedo calculator for type VIIC U-Boats with drying sockets visible at the front panel

Kalkulator torpedowy w kiosku U 505 z widocznym gniazdem przeznaczonym do osuszania wnętrza na lewej ściance

Photo 13. Torpedo calculator in U 505's conning tower with a drying socket visible at the left side [10]

Kalkulator torpedowy przeznaczony dla U-Bootów typu IXC z widocznym gniazdem przeznaczonym do osuszania wnętrza na prawej ściance

Photo 14. Torpedo calculator for type IX U-Boats with a drying socket visible at the right side [9]

 

Also in this case, one can suspect, that this difference resulted from final location of the device. In the type VIIC U-Boat conning tower, connecting the drying pipe to the socket at the top side would be difficult because of the guide-bar for the attack periscope winch cables;

  • The torpedo calculators for the type XB U-Boats (which were armed with two stern torpedo tubes only) were not fitted with parallax switch (vorn/achtern). Presumably, calculators for the type II U-Boats did not have this switch also.

Kalkulator torpedowy w kiosku U 234 (U-Boot typu XB)

Photo 15. Torpedo calculator in U 234's conning tower (type XB U-Boat)

  • the torpedo calculators for different types of U-Boats were fitted with different 3-dimensional cams inside the component for calculating the parallax correction. It resulted from different distances between the periscopes and the torpedo tubes. From this distance depended coordinates of the equivalent point of fire.

The innovate type XXI U-Boats were intended to be fitted with a quite new torpedo fire control system. This new system would allow for blind launching torpedo, without usage of the periscope, only on the basis of acoustic bearings. When the first Electro-boats entered the service, it turned out that the development of the fire control system was not completed. In such situation, Germans decided to use type T. Vh. Re. S3 torpedo calculator. 

Kalkulator torpedowy przeznaczony dla U-Bootów typu XXI

Photo 16. Torpedo calculator for type XXI U-Boats [11]

 

The calculator was installed in the conning tower (similarly as on type IX and XB). Similarly, as in case of the calculators for type XB U-Boats, it was not fitted with the parallax switch (vorn/achtern), because Electro-boats were armed only with bow torpedo tubes. On the photo one can see, that the angle of impact control lamp is embedded directly into the front panel, not into the protruding cap as in case of earlier versions. Presumably, this modification required some rearrangement of the calculator internals. 

In the final years of the war, three other modifications were introduced. These improvements were required by new type of the torpedo, that just entered the service (a pattern-running LUT torpedoes). These modifications will be described in the one of next articles.

 

References:

[1] Lawrence Paterson, U-Boat War Patrol: The Hidden Photographic Diary of U 564
[2] Jacques Alaluquetas, U-Boot VII C : Technique - Construction – Armement
[3] Report on the interrogation of survivors from U 172 sunk 13 December 1943
[4] Report on the interrogation of survivors from U 177 sunk 6 February 1944
[5] Report on the interrogation of survivors from U 575 sunk 13 March 1944
[6] Report on the interrogation of survivors from U 841 sunk 17 October 1943 and U 848 sunk 5 November 1943
[7] Eckard Wetzel, U 995
[8] Museum of Science and Industry, Chicago, U 505 Submarine
[9] Edward Monroe Jones, Shawn S. Roderick, Submarine Torpedo Tactics: An American History
[10] Museum of Science and Industry, Chicago, The Story of the U 505
[11] Torpedo Fire Control Installation in U-Boats Type XXI, 1944