From
www.uboat.net:
U-23
Type IIB
Ordered 2 Feb, 1935
Laid down 11 Apr, 1936 Germaniawerft, Kiel (werk 553)
Launched 28 Aug, 1936
Commissioned 24 Sep, 1936
Commanders 1 Sep, 1936 - 3 Jan, 1938 KrvKpt. Eberhard Godt
1936/37 - 30 Sep, 1937 Hans-Günther Looff
1 Oct, 1937 - 1 Apr, 1940 Kptlt. Otto Kretschmer (Knights Cross)
8 Apr, 1940 - 19 May, 1940 Kptlt. Heinz Beduhn
20 May, 1940 - 30 Sep, 1940 Heinrich Driver
1 Oct, 1940 - 20 Mar, 1941 Kurt Reichenbach-Klinke
21 Mar, 1941 - 23 Sep, 1941 Ernst-Ulrich Brüller
24 Sep, 1941 - 26 Mar, 1942 Ulrich Gräf
27 Mar, 1942 - 19 Jun, 1944 Kptlt. Rolf-Birger Wahlen
20 Jun, 1944 - 10 Sep, 1944 Oblt. Rudolf Arendt
Career 16 patrols 1 Sep, 1936 - 1 Aug, 1939 1. Flottille (front boat)
1 Sep, 1939 - 31 Dec, 1939 1. Flottille (front boat)
1 Jan, 1940 - 30 Jun, 1940 1. Flottille (front boat)
1 Jul, 1940 - 30 Sep, 1942 21. Flottille (school boat)
1 Oct, 1942 - 10 Sep, 1944 30. Flottille (front boat)
Successes 7 ships sunk for a total of 11.179 GRT
2 warships sunk for a total of 1.410 tons
1 auxiliary warship damaged for a total of 1.005 GRT
1 warship damaged for a total of 56 tons
3 ships a total loss for a total of 18.199 GRT
Fate Scuttled at 2210hrs on 10 Sept, 1944 off the coast of Turkey in the Black Sea in position 41.11N, 30.00E.
U-20
Type IIB
Ordered 2 Feb, 1935
Laid down 1 Aug, 1935 Germaniawerft, Kiel (werk 550)
Launched 14 Jan, 1936
Commissioned 1 Feb, 1936 Kptlt. Hans Eckermann
Commanders 1 Feb, 1936 - 30 Sep, 1937 Hans Eckermann
1 Oct, 1937 - 17 Jan, 1940 Kptlt. Karl-Heinz Moehle (Knights Cross)
17 Jan, 1940 - 15 Apr, 1940 Kptlt. Harro von Klot-Heydenfeldt
2 Apr, 1940 - 15 Apr, 1940 Heinrich Driver
16 Apr, 1940 - 7 Jun, 1940 Hans-Jürgen Zetzsche
8 Jun, 1940 - 5 Jan, 1941 Ottokar Arnold Paulshen
6 Jan, 1941 - 19 May, 1941 Kptlt. Herbert Schauenburg
20 May, 1941 - 4 Dec, 1941 Wolfgang Sträter
5 Dec, 1941 - 27 Mar, 1942 Kurt Nölke
7 May, 1942 - 26 Sep, 1942 Clemens Schöler
27 May, 1943 - 31 Oct, 1943 Kptlt. Clemens Schöler
1 Nov, 1943 - 10 Sep, 1944 Oblt. Karl Grafen
Career 17 patrols 1 Feb, 1936 - 1 Aug, 1939 3. Flottille (front boat)
1 Sep, 1939 - 31 Dec, 1939 3. Flottille (front boat)
1 Jan, 1940 - 30 Apr, 1940 1. Flottille (front boat)
1 May, 1940 - 30 Jun, 1940 1. U-Ausbildungsflottille (school boat)
1 Jul, 1940 - 30 Sep, 1942 21. Flottille (school boat)
1 Oct, 1942 - 10 Sep, 1944 30. Flottille (front boat)
Successes 13 ships sunk for a total of 30.067 GRT
1 ship damaged for a total of 1.846 GRT
2 ships a total loss for a total of 8.446 GRT
Fate Scuttled at 2130hrs on 10 Sept, 1944 off the coast of Turkey in the Black Sea in position 41.10N, 30.47E.
U-19
Type IIB
Ordered 2 Feb, 1935
Laid down 20 Jul, 1935 Germaniawerft, Kiel (werk 549)
Launched 21 Dec, 1935
Commissioned 16 Jan, 1936 Kptlt. Viktor Schütze (Oak Leaves)
Commanders 16 Jan, 1936 - 30 Sep, 1937 Kptlt. Viktor Schütze (Knights Cross)
30 Sep, 1937 - 1 Nov, 1939 Hans Meckel
2 Nov, 1939 - 2 Jan, 1940 Wilhelm Müller-Arnecke
3 Jan, 1940 - 30 Apr, 1940 Kptlt. Joachim Schepke (Knights Cross)
1 May, 1940 - 19 Jun, 1940 Wilfried Prellberg
20 Jun, 1940 - 20 Oct, 1940 Peter Lohmeyer
21 Oct, 1940 - 8 Nov, 1940 Wolfgang Kaufmann
8 Nov, 1940 - 31 May, 1941 Rudolf Schendel
1 Jun, 1941 - Feb, 1942 Gerhard Litterscheid
16 Dec, 1941 - Feb, 1942 Hans-Ludwig Gaude
Feb, 1942 - 30 Apr, 1942 Hans-Ludwig Gaude
1 Oct, 1942 - 2 Dec, 1943 Kptlt. Hans-Ludwig Gaude
3 Dec, 1943 - 6 Sep, 1944 Oblt. Willy Ohlenburg
7 Sep, 1944 - 11 Sep, 1944 Oblt. Hubert Verpoorten
Career 20 patrols 1 Jan, 1936 - 1 Aug, 1939 1. Flottille (front boat)
1 Sep, 1939 - 31 Dec, 1939 1. Flottille (front boat)
1 Jan, 1940 - 30 Apr, 1940 1. Flottille (front boat)
1 May, 1940 - 30 Jun, 1940 1. U-Ausbildungsflottille (training)
1 Jul, 1940 - 18 Dec, 1940 24. Flottille (training)
19 Dec, 1940 - 1 May, 1942 22. Flottille (school boat)
1 Oct, 1942 - 11 Sep, 1944 30. Flottille (front boat)
Successes 14 ships sunk for a total of 35.430 GRT
1 warship sunk for a total of 441 tons
Fate Scuttled at 2230hrs on 11 Sept, 1944 off the coast of Turkey, Black Sea in position 41.34N, 31.50E.