Authentic speed measurement in SH4

[joegrundman]

I think that's very interesting Joe Armstrong, but as you say data was incomplete for this to be a comprehensive method even later in the war

Here's what the 1950 submarine torpedo fire control manual has to say about it:

TURN COUNTThe Approach Officer should have available for ready reference the most complete set of curves that he can obtain of different types and classes of enemy vessels. Their use will furnish a means of approximating the speed of an observed target.
Due consideration must, of course, be given to wind and sea conditions and condition of loading as they increase or decrease the speed of any given R.P.M. Turn count is most valuable in determining a sudden change of target speed.



and a bit further on it says

(b) Although five methods of determining speed have been given above, it still remains that under almost all circumstances Plot and TDC are the two primary methods which the submarine must employ to obtain target speed. In both of these methods any error in underwater log speed will introduce a corresponding error in solution of target speed.

Now this is written in 1950, 5 years after the war finished, and with 5 years more experience and technological improvement and it makes it clear that turn count was not considered the primary speed determination method.

Referencing variations in wind and sea state as well as loading, and emphasising that turn count is most useful for registering changes in target speed, rather than an accurate estimate of target speed - one should ask before assuming that this is how it ought to be done in game, HOW ACCURATE WAS THIS METHOD AT THE TIME?

I think from this manual we can conclude that at the time, turn count was considered a supplementary source of speed estimate by the USN, and not a primary one - and the only reason this could be is that it was less reliable in most circumstances, with the technology of the day.

However, it is also clear that they were striving to improve the estimates furnished by this method.

ref for the manual: http://hnsa.org/doc/attack/index.htm