Armament
     
  Target Identification  
          Identifying the target was important for applying the rules of engagement, firing calculations, intelligence accounting, and for submitting the correct claim for tonnage.  If the tactical situation allowed, the CO would observe the target, noting the ship's characteristics while First Watch Officer or Obersteuermann refered to Dr. Erich Gröner's Die Handelsflotten der Welt or Weyers Taschenbuch der Kriegsflotten These compact publications privided details of all merchant and warships ships known to the German Navy.  
   
 

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Excerpt from Dr. Erich Gröner's Die Handelsflotten der Welt
 
     
  Torpedo Tubes  
          Type VII and IX U-boats had four bow torpedo tubes. Type VII had one stern tube while Type IX had two. There were a few exceptions for both types and special purpose boats such as supply boats, torpedo carriers and mine layers had different configurations.  The tubes were usually referred to in KTBs by Roman numerals (Rohr I, II, III, IV, V, VI) – bow tubes numbered 1, 2, 3, 4, stern tubes numbered 5 and 6 (odd numbered tubes to starboard, even numbered tubes to port - in the bow room tubes 1 and 2 upper, tubes 3 and 4 lower).  All German U-Boat torpedo tubes were 53.3 cm/21" in diameter and 7.16 meters long.  A close fit piston weighing 75 lbs. was placed behind the torpedo after loading.  Firing was by compressed air from a low pressure reservoir at 29 atmospheres.  A pressure of approximately 16.3 atmospheres was used for surface firing, 10.5 for submerged firing.  For submerged firing the compressed air acted against the piston forcing the torpedo from the tube at a speed of 10 meters/second.  A relief valve automatically opened at the back of the tube and water pressure would force the piston back to its original position venting the compressed air back into the boat.  For surfaced firing the compressed air was directed between the piston and the torpedo by means of a change-over cock which also locked the piston to the tube. After firing the forward tube door was closed and the water drained into the bilge.  The tube was then ready for loading.   
     
  Torpedo Types  
          Often referred to in KTBs as simply Ato or Eto (A for Air and E for Electric) further details were left to the torpedo firing report (Schussmeldung).  The Ato burned a mixture of compressed air, water and Decalin in a radial engine for propulsion leaving a visible bubble trail on the surface.  The Eto used a battery for propulsion and left no bubble trail on the surface.  The table below provides information on the most common types of torpedoes carried aboard U-boats.  
 
Type
Date in Service
Guidance
Pistol
Propulsion
Weight (kg)
Range (km)
Speed (knots)
T I
G7a
1938
Straight
Pi 1 or TZ3 with Pi 3
4-cycle  gas/steam
1,538
7.5/12
40/30
T I Fat I
G7a
late 1942
Fat
Pi 1 or TZ3 with Pi 3
4-cycle  gas/steam
1,538
7.5/12
40/30
T I Lut I/II
G7a
late 1944
Lut
Pi 1 or TZ3 with Pi 3
4-cycle  gas/steam
1,538
7.5/12
40/30
T II
G7e
1939
Straight
Pi 1
Electric
1,608
5.0
30
T III
G7e
late 1942
Straight
Pi 2
Electric
1,608
5.0
30
T III Fat
G7e
mid 1943
Fat
Pi 2
Electric
1,700
5.0
30
T IIIa Fat II
G7e
early 1944
Fat
Pi 2
Electric
1,620
7.5
30
T IIIa Lut I/II
G7e
early 1944
Lut
Pi 2
Electric
1,760
7.5
30
T IV Falke
G7es
early 1943
Acoustic homing
Pi 4a
Electric
1,400
7.5
20
T V Zaunkönig
G7es
late 1943
Acoustic homing
TZ 5 with Pi 4c
Electric
1,495
5.7
24
  Note:  Torpedoes could be directed to turn up to 90° off initial course in 1° increments (later changed to 135°).  Depth settings were 0-12 and later 0-15 meters in one meter increments.  Torpedoes were designed to sink at the end of the run without detonating.  To obtain optimum performance from G7e torpedoes batteries had to be withdrawn from the torpedo tubes and serviced every few days and the battery had to be heated to 30°C/85°F just prior to firing (if not only 28 knots at 3,300 meters could be obtained).  
     
  Fat and Lut Steering Mechanisms  
          Fat, short for Federapparat Torpedo, was a steering mechanism which enabled the torpedo to begin a ladder pattern at a preset point of a normal run.  The Fat I torpedo could be set to turn 180° right or left on short (900 yds/820 meters) or long (1,640 yds/1500 meter) legs.  The speed of advance when set for short legs was 7 knots and for long legs 5 knots.  The Fat II, in tended as a self defense weapon, could be set to describe a long loop or a circle (always to the left) at a preset point in its initial normal run.   The Lut, short for Lagenunabhängiger Torpedo, could be set for an additional course change after the initial normal run.  This allowed the U-boat to launch from any position relative to the target.   The Lut I enabled the length of the ladder legs to be set between 0 and 1500 meters.  Thus the speed of advance could be varied between 5 and 21 knots.  The Lut II enabled the left or right turns to be set at angles less than 180°   See the following excerpt from the Admiralty Cumulative Edition for additional information on Fat and Lut torpedoes.  
     
 

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Excerpt on Torpedoes from the Cumulative Edition - CB 04051(103) The Admiralty's appreciation of the German U-boat force as of June 1944
 
     
  Torpedo Pistols  
Date in Service
Fuse
Used with
Pi G7a
from 1934
 Both Impact (AZ) and Magnetic (MZ) (Modified in October 1939 to allow firing in AZ only) - the MZ feature had 16 zones (-5 to 16) to compensate for variation in the strength of the earth's magnetic field.  A special chart was consulted to select the zone (0 for Norway's North Cape to 16 for the Bay of Biscay) which was set by means of a movable ring on the front of the pistol. G7a and G7e
Pi G7a (A+B)
November 1939
A modification of the Pi G7a pistol designed to reduce the possibility of premature detonation G7a and G7e
Pi 1 (Pi G7H)
Summer 1940
Impact only.  This was the standard German pistol from the summer of 1940 until the end of 1942. G7a and G7e
Pi 2 (Pi 39H)
December 1942
Selectable impact and magnetic or impact alone (new German designed magnetic detonator - impact mechanism same as Pi1) G7e TIII
TZ3 with Pi 3
Late 1943
Selectable impact and magnetic or impact alone (TZ3 based on the Italian SIC magnetic pistol - impact mechanism same as Pi 1) G7a
Pi 4
late 1943
Inertia T IV
TZ5
early 1943
Magnetic T V together with Pi 4
  Note:  Pi 1, 2, and 3 pistols armed the torpedo after it had travelled 250 meters (after June 1940 150 meters) from the U-boat.  T IV and T V torpedoes armed at 250 meters after firing.  
   
  Torpedo Warheads  
          G7a and G7e torpedoes were fitted with a warhead weighing 617 lbs/280 kg  The explosive was a mixture of hexanitrophenylamine (NHD) and trinitrotoluene (TNT) mixed 25% by weight with aluminum (Al) or TNT/HND/AI for short.  The T IV and T V torpedoes had a slightly smaller warhead, 604 lbs/274 kgt, to accommodate the acoustic homing mechanism in the nose and the cavity for the pistol.  
     
  Torpedo Firing Reports  
          Each time a torpedo was fired the Commander was required to submit a torpedo firing report.  The purpose of the report was to enable the Torpedo Inspectorate (Torpedoinspektion (T.J.)) to analyze and track torpedo performance.  The form was usually filled out by the First Watch Officer who also served as Weapons Officer.  The report included a description of the weather and target; type of torpedo and pistol, torpedo tube and ejection method; source of firing data, aim point and firing values; all torpedo and pistol settings; the position of the boat relative to the target; and the observed performance of the torpedo.  On the reverse of the report there was a narrative description of the tactical situation and often a diagram depicting the position of the boat relative to the target at firing and the track of the boat up to firing.  These reports were included as an attachment to the KTB and are a valuable supplement to the brief description of an attack typically found there.  See the following page for more information on torpedo firing reports.  
 

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Torpedo Firing reports - Keys, notes and examples
 
     
  Guns  
          The table below provides information on guns carried aboard U-boats.  
Caliber
Type - Mount
Breech/ Clip
Practical rate of fire
Maximum Elevation
Effective Range
Gun's Crew
Weight of Projectile
               
Deck guns              
105 mm (4.14")
SK C/32U - U-boat L C/32U
Single-shot
15
35°
12,000 m.
6
 51.4lbs/23.3kg
105 mm (4.14")
SK C/32U - 88mm Marine Pivot L C/30D
Single-shot
15
30°
12,000 m.
6
 51.4lbs/23.3kg
 
30°
88 mm (3.46")
SK C/30U - U-boat L C/30U
Single-shot
15-18
80°
11,000 m.
6
 30.11lbs/13.7kg
88 mm (3.46")
SK C/35 - U-boat L C/35U
Single-shot
15-18
30°
11,000 m.
6
 30.11lbs/13.7kg
 
Anti-aircraft guns            
37 mm (1.46")
SK C/30U - Ubts. LC 39
Single-shot
12
85°
2,500 m
3/4
1.6lbs/730g
37 mm (1.46")
M42 U - LM 43 U
Automatic 8-round
40
80°
2,500 m
3/4
1.6lbs/730g
Twin 37 mm (1.46")
Zwilling M 42 U - LM 42
Automatic 8-round
80
80°
2,500 m
3/4
1.6lbs/730g
30 mm for Type XXI Flak M 44 - LM 44 Automatic
20 mm (0.79")

AMG C/30 - L 30
Automatic 20-round
120
90°
1,500 m
2/4

0.7 lbs/320g

20 mm (0.79")
MG C/30 - L 30/37
Automatic 20-round
120
90°
1,500 m
2/4

0.7 lbs/320g

20 mm (0.79")
Flak C/38 - L 30/37
Automatic 20-round
220
90°
1,500 m
2/4

0.7 lbs/320g

Twin 20 mm (0.79")
Flak Zwilling C/38 II - M 43 U
Automatic 20-round
440
90°
1,500 m
2/4

0.7 lbs/320g

Quadruple 20 mm (0.79")
Flak Vierling C38/43 - M 43 U
Automatic 20-round
880
90°
1,500 m
2/4

0.7 lbs/320g

       
Twin 13.2 mm (0.52") Breda 1931 - retractable into water-tight housing
Automatic 30-round
400
85°
1,000 m
2/4
0.28 lbs. 125g
               
Self defense guns
           
7.92 mm
MG15
Automatic 50/75 round
800-900
90°
750 m
1-2
12.8g
7.92 mm
MG34
Automatic 50/75 round
600-700
90°
750 m
1-2
12.8g
Twin 7.92 mm
MG81Z
Automatic Belt fed
2,200
 90°
750 m
1-2
12.8g
Additionally a variety of small arms were carried, typically 5-10 Mauser 7.65 mm pistols, 5-10 rifles, submachine guns (MP-40 - 9 mm), hand grenades, and 2 signal pistols.