The first letter indicates the diameter:
The number indicates the approximate length (for example, the length of the TI is 7163 mm):
Next letter(s) indicates specific features regarding propulsion and control:
"r" and "t" were only used with "u" to further denote the features of the ingolin-torpedoes. Some sources claim that "s" only was used with "a" to denote the development of G7a with acoustic seeker-capability; however, it was no doubt used for the electric torpedoes with acoustic seekers (as "es" or just "s").
When the torpedo reached production status and was fielded (i.e. for operational use), Kriegsmarine gave it a short designation "T", or "Torpedonummer", with the number given in Roman lettering (TI, TII, TIII, TIV, etc.). For different versions of the main torpedo, a small Arabic letter was added (for example TIIId, TVa etc.) denoting changes from the main design.
Warheads were designated with the letter "K" (K = short for Kopf, meaning "head") and a small Arabic letter, with an additional number denoting variants of the head (for instance changing the material composition from bronze to steel, adding/removing spants during the course of the war or the method of installing the explosives). Examples: Ka, Ka1, Kb, Kb1, etc.
The explosive charge of warheads in German torpedoes during WW2, were different compositions of the Schießwolle (SW) that consisted mainly of a mixture of Trinitrotoluene (TNT) and Hexanitrodiphenylamin (HND):
A total of 41 different types of explosive charges were used in German underwater ordnance, all given a "S"-number (1-41) for identification (only those relevant for torpedoes are listed here):
List of Kriegsmarine warheads with weight/type of explosive charge:
Pistols used the "Pi" designations to begin with (Pi = short for pistole). The early models were named according to function and/or torpedo type like "PiG7H" or "PiG7A-MZ", but this was later replaced with a simple system of numbers, like "Pi1", "Pi2" etc.
To indicate variants within the main design, a small Latin letter was added after the number, like "Pi1a", "Pi1b" etc.
At some point, "Pi" was dropped for pistols with combination of mechanical (direct hit) and magnetic (influence) mechanisms, to the "TZ" designation (TZ = Torpedo-Zündeinrichtung). For example, the mechanical mechanism from the "Pi1" pistol combined with the magnetic mechanism from "Pi2" became the "TZ2".
The main booster charge used in German pistols was Pentrite, typically 300 g.
The following torpedopistols reached operational status with Kriegsmarine during WW2:
Code names were intended to be used only through the development period for security measures. However, in some cases they remained after the torpedo was fielded and had been designated with a "T"-number.
Torpedo pistols, program seeker-systems and other special arrangements also had their own "system" of code names, using the names of birds, fish or animals (for example Pi "Leuchtfisch", GA "Specht", seeker "Storch", control "Viper", target detector "Salamander" etc.). During development, the pistols were often given code names designated by the industrial developer or manufacturer. Generally, these consisted of simple words, syllables, or names associated with the firm or the engineers in charge of the pistol's development (for example Pi "Otto", Pi "Atlas", Pi "Berlin" etc.).
Program steering was accomplished by a mechanical device ("Federapparat") coupled to the torpedo's gyroscope to alter its course in various pattern. Two main types was fielded during WW2: "Fat" and "Lut".
Fat ("Flächenabsuchender Torpedo"): Changed the torpedo's course over time so that it ran various patterns. Three versions: Fat I, II and III (Fat III was later redesignated Lut I).
Lut ("Lageunabhängiger Torpedo"): Similar to Fat, but changed the torpedo's course to a preset heading directly after launch, so the launching platform could fire torpedoes at targets without changing its own course. Two versions: Lut I and Lut II (+ a special Lut I variant for the TIIId torpedo with a very long initial straight run of 36000 m).
The Fat or Lut mechanisms initiated control of the gyroscope after an initial (preset) straight running distance.
Fat I ("S-shaped" loop-patterns): The initial straight distance could be set from a minimum of 500 m to a maximum of 1500 m. Two loop-patterns were available: "short" and "long", and in addition, there was a choice of right or left turns (i.e. a total of 5 settings on the Fat-mechanism). For "short" loops, the straight distance between turns was 800 m, with a total width of the pattern-search of 1140 m For "long" loops, the straight distance between turns was 1500 m, and a total width of the pattern-search of 1840 m. The turning radius for both patterns was 170 m.
Fat II ("S-shaped loops or circular patterns): The same as Fat I, but with an additional choice for "circular pattern", where the torpedo would run in a circle after the initial straight-run. This was an option primarily used by U-boats against attacking surface-ships that ran a zig-zag pattern hunting the U-boat (the goal was to locate the torpedo's circle-run just ahead of the attacking ship, hoping for a "lucky" hit).
Fat III / Lut I ("zig-zag" pattern): Initial torpedo course could be chosen, so the torpedo platform did not need to change its bearing to an optimal course for torpedo launch. The "Lut-speed" (i.e. the resulting advance-speed of the torpedo, considering the zig-zag pattern) could be chosen, and subsequently, the straight legs between turns would be adjusted accordingly.
Lut II: Same as Lut I, but even slower Lut-speeds could be chosen.
As a general rule, Luftwaffe followed the Kriegsmarine system of code names and designations, but with some differences.
Variations for the letter(s) indicating specific features regarding propulsion and control:
Instead of letters and numbers denoting dimensions and features, a single 3 or 4 digit number was used for some torpedo designs.
Luftwaffe used the "LT" designation (= Lufttorpedo), but not limited to operational torpedoes. It also combined further letters and numbers to indicate type and features of the torpedo:
Luftwaffe warheads were designated GK (= Gefechtskopf) followed by a number and a small Arabic letter for variants. Exerciseheads was designated ÜK (= Übungskopf). The various types of explosives are described under the section of Kriegsmarine warheads above.
Operational warheads (weight/type of explosive charge):
Warheads in various state of development/test and production by end of the war (weight/type of explosive charge):
Designations for Luftwaffe pistols used the same system as Kriegsmarine.
The following torpedopistols reached operational status with Luftwaffe during WW2:
Luftwaffe also developed a passive weapon called "Bombentorpedo" (BT), which was planned to replace the conventional torpedoes. It was airdropped from a low height and relative short distance from the target, would enter the water and travel the short remaining distance solely driven by its kinetic energy. No BT's were ever fielded operationally.
Various aircraft designed for/configured as torpedo carriers: