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From: nuchat!steve@uunet.UU.NET (Steve Nuchia)
Newsgroups: sci.military
Subject: Re: WWII Submarine Navigation and Attack Terminology
Message-ID: <1990Oct1.022124.3251@cbnews.att.com>
Date: 1 Oct 90 02:21:24 GMT
References: <1990Sep24.002015.24721@cbnews.att.com>
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From: nuchat!steve@uunet.UU.NET (Steve Nuchia)

>From: r_anderson@flyppr.enet.dec.com
>1.  When a target's bearing is "marked" through the periscope,
>is the angle relative to submarine (0 degrees being the bow, 180
>degrees being the stern), or relative to the "true" geographic
>course?

The bearing coming off the 'scope is relative, but the boat knows
her heading, so conversion is trivial -- just add the relative
bearing to the true heading, modulo 360, and you have a true
bearing.  The relative bearing is dialed into a target computer
(analog, of course) which has a true heading input as well, and
it figures it all out for you.  There is probably a backup computation
going on using graphical techniques on paper, but I am not familiar
with the details.

That was WWII.  Today you normally don't use the scope for targeting,
you fire on a solution derived from passive sonar data, and it is
probably computed digitally.

>2.  Can someone clearly explain the term "angle on the bow" and
>how this information is useful in determining a torpedo attack?

A torpedo targeting solution is derived from a series of sightings,
each of which is taken from a particular spot on the ocean and
returns bearing and estimated range to the target, and an estimate
of the direction the target is travelling.  This last datum is
based on the "angle on the bow", the relative bearing of the
observer from the target.  A good skipper can call that angle
within 10 degrees.  A bow angle of 000 means you are looking
at the target head on, 090 you are broad on her starboard beam, etc.

The targeting computer takes the time-series of sighting data
and fits an assumed straight-line, steady speed target course to
it.  Usually after the solution is computed and you are ready to
fire you take one more confirming peek -- if the target is exactly
where the computer predicts it should be you have a good solution,
and you fire.

>3.  Can someone clearly explain what an "Is-Was" is and how it
>works?

>4.  Can someone clearly explain what a "TDC" is and how it works?

Not familiar with the terminology, sorry.
-- 
Steve Nuchia	      South Coast Computing Services      (713) 964-2462
"To learn which questions are unanswerable, and _not_to_answer_them;
this skill is most needful in times of stress and darkness."
		Ursula LeGuin, _The_Left_Hand_of_Darkness_