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What is this thing and why do I need one?

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oldsubs View Drop Down
Neptune
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    Posted: 27 Jan 2019 at 9:27pm
What is a device called a "stable vertical", what exactly does it do and if it is a part of another device, what device?

What submarine might have need of such a device and which submarine(s) had it installed, if any.

Hint: It is not part of the FBM missile fire control system nor part of the SINS navigation system.



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Post Options Post Options   Thanks (0) Thanks(0)   Quote whalen Quote  Post ReplyReply Direct Link To This Post Posted: 27 Jan 2019 at 10:34pm
Was it in the lower lever of AMR-1?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote oldsubs Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan 2019 at 7:34am
No it wasn't.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tom McNulty Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan 2019 at 10:28am
You were thinking of the big mamu gyro?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 609EM1 Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan 2019 at 12:20pm
Hope this is close....I wasn't an FTG.

A "stable vertical" is a vertical seeking gyroscope that supplies the gun fire control system with a stable up direction on a rolling and pitching ship.

Most submarines lacked effective surface fire control systems, but seven submarines (SS-229, 340, 399, 401, 406, 407 and 408) were converted to "gunboats" during 1945. These boats carried two 5"/25 (12.7 cm) guns, a Mark 6 stable vertical, a Mark 6 computer and a gun plot installed in the forward crew quarters. The computer drove repeaters at the guns.


Edited by 609EM1 - 28 Jan 2019 at 12:26pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote oldsubs Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan 2019 at 1:18pm
It is correct. 

Now, why is it needed?  If the gun is being aimed over 'open sights' what could knowing when the gun is vertical matter? 

Is is needed more for a two gun installation than for a single gun? 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote oldsubs Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan 2019 at 5:28pm
Ok, I am going to explain since I am going to be off the bbs for a week or so. 

When you aim a gun over open sights it is usually at a short range.  For the submarine deck guns it was little over 2000 yards (about  a nautical mile).  Beyond that, several errors rear their ugly head and cause an extraordinary number of misses. 

To hit the target you have to know the range so you know how far above the target to aim to allow for bullet drop.  To find the range you need to have a 'range finder'.  Use it and you determine the range. 

To determine the deflection (relative bearing to point the gun) you simply need to line up the target with a vertical sight line on you gun. 

So far so good.  If the ship is stable you determine the range and deflection, point the gun accordingly and shoot.  If the ship is not stable all bets are off.  The barrel is a long tube which waves around as the ship rolls and pitches.  The trunions on which the barrel is mounted tilt one way and another.  Some of the trunion tilt is given by the roll some by the pitch.  This trunion tilt causes the barrel to wave about.  You can measure this trunion tilt and thus which way the barrel is pointed relative to the instruments used to aim the gun.  This is called obtaining the 'cross level'.  The cross level measurement depends on the exact roll and pitch of the ship.  This then depends on knowing some fixed reference on the ship.  The bubbles are too inaccurate and too slow and the gyrocompass is not set up to feed a true vertical signal to the aiming fire control although it could be.  In the stable element is a gyro that is set up to measure the ships departure from zero roll and zero pitch. It is the stable vertical that provides this zero bubble, zero roll reference.  The signal sent to the gun via instrumentation called the stable element which allows the trainer and pointer to move the gun to compensate for the pitch and roll.  Or, as is more accurate, the fire control system for the gun with the stable element can be set up to fire the gun automatically when the gun crosses zero pitch and zero roll. You tell the fire control system when you are ready to fire and the system takes over from there. Thus taking out the 'gunners eye' method of firing when he thinks the time is right.

During WWII when the concept of the gunship submarine was being formulated, it was necessary to use a more accurate form of fire control to gain an increased range and accuracy.  For two-gun ships, the fire control system also took into account the parallax angle of the two guns firing at the same target.

All modern gun fire control systems use some form of the stable vertical and stable element.  In addition the system must compensate for windage, earth's rotation, ballistics of the gun and projectile such as barrel droop, drag, temperature effects on propellant and so on. 

We submariners on the other hand simply invented a torpedo that could be steered then it listened for a target signature and steered itself then went active and scared the hell of the enemy before impact.  Ours is the simpler method. 

For more information google some books by Norman Friedman on naval weapons. 

Till next time

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