Generally speaking, the mminimum torpedo tube length is set by the weapon, the actual tube length by the layout of the tube in the boat.



An excellent reference for USN fleet boats can be found at:

[www.maritime.org]



and on pages 18 and 19 we find:

"finish the tube to the diameter of 21.125 inches,"

and

" torpedo tubes are of two lengths, bow tubes being 252 inches, stern tubes 276 inches, over all length, not including doors. The effective length (the greatest length of the torpedoes that can be loaded into the barrel) for a barrel 252 inches over-all would be 250.81 inches; for a barrel 276 inches over-all, the effective length would be 274.81 inches"

on page 124 we find that:

"Torpedoes are divided into three groups according to the location of the guide stud, the distances from the tail to the front of the guide stud being 109.0 inches, 141.44 inches, or 150.44 inches, depending upon the length of the torpedo,"

and

"The torpedo tubes described in this pamphlet were designed primarily for the Mark 14 torpedo, which has the front of the guide stud 141.44 inches from the end of the tail, hence they will accommodate such torpedoes without any adjustment or alteration of either the tube or the torpedo. The length of this torpedo has been increased to 246.0 inches, but this increase in length does not in any way affect the operation of the torpedo tube."


Seems like some definitive answers on German tubes and fish were provided, in metric units. Conversions to English units and rounding errors may explain the confusion. Thus:

53.46cm / 2.54 cm/in = 21.047 inches - rounded to 21 inch, and then back

21 inch * 2.54 cm/in = 53.34 cm - rounded to 53.3 cm


Dan