September 29, 2021

Pictures - Iowa Main Battery Plot

It's finally time for our long-running photo tour of Iowa to reach my favorite space, the plotting rooms. The main and secondary battery computers are in separate, adjoining spaces, and can be visited on special tours. I'm usually too busy with certain activities (seen below) to take many pictures, so these were taken over half a dozen visits.

Despite this, I ended up with enough pictures to split this into separate posts for the main and secondary battery plots. This will cover the main battery plot. For a full explanation of how everything works, see here.

Entrance to the main battery plot is through this door. Note the bolts around it, which allow this section of wall to be opened up for moving large pieces of equipment in and out. Iowa's ops team recently did this to install the Mk 48 shore bombardment computer.

There are three main pieces of equipment in the main battery plot: the Stable Vertical (a fancy gyroscope that compensates for the angular motion of the ship), the Mk 8 Rangekeeper (which compensates for the linear motion of the ship and its target) and the Mk 48 Shore Bombardment Computer, which is a very primitive moving map for use when shooting at shore targets.

The Stable Vertical.

The firing triggers on the stable vertical. The left trigger is pulled to warn everyone that a salvo is about to be on its way, while the right ones actually fire. If in manual mode, the guns fire immediately, while in automatic, the circuit is completed when the guns are in the right position as the ship rolls and pitches. Note that the grips are differently-shaped, so you can tell them apart by touch.

This indicator shows which turrets are ready to shoot.

The inside of the Stable Vertical. There's mercury in there, so I'd recommend not eating anything you find inside.

The Mk 8 Rangekeeper.

The top of the Mk 8, showing the displays, as well as the knobs you can use to manually input information. They still work, and the whole thing runs smoothly.

The Mk 48, installed fairly recently after Wisconsin stole the one originally in this space, was designed after WWII to improve shore bombardment performance.

A map would be placed on top of it (underneath the cover in this picture), and a dead-reckoning system would project the ship's location as a moving dot of light.

Tying it all together is the switchboard, which allows different systems to be cross-connected, even between the main and secondary batteries.

There are a few lockout tags on the switchboard dated April 1989.

One last object of interest is the equipment for the Mk 13 fire-control radar atop the main battery directors.

These are B-scopes, not the classic PPI.


  1. September 29, 2021ike said...


    I don't quite know how to say this, but are you cuddling that very expensive electro-mechanical device in the first picture?

  2. September 29, 2021bean said...

    Yes. Yes I am.

  3. September 29, 2021ike said...

    Well, I want you to know, on behalf on everyone here, we still love you and won't tell your wife.

  4. September 29, 2021Directrix Gazer said...

    I understand, Bean. I have an almost identical picture of me with a W9 atomic shell at the Watervliet Arsenal museum.

  5. September 29, 2021Emilio said...

    Bad, bad Wisconsin!

  6. September 29, 2021Emilio said...

    I'd hate being the one undoing and redoing all those bolts.

  7. September 29, 2021nomad said... has info on the Mk48 including the tech manuals.

  8. September 30, 2021ike said...


    I don't know. I think I would take being to guy with the wrench over lugging the heavy equipment through that opening.

  9. September 30, 2021tim shatz said...

    Depends if you need the bolts off in a hurry or it's a yard job tasked out for days. Yard job involves smoking, shooting the shit while doing the bolts one at a time. No hurry, just move along smoothly.

    But if it's in a hurry, then the things will stick, you'll lose gaskets, the wrench won't quite fit, someone will be telling you to "hurry the f**k up". Murphy's law applies.

  10. September 30, 2021bean said...


    The designers made provisions for moving stuff like that in and out. There are lifting points on the ceiling, overhead rails, and various other aids. One of my friends was on the crew that brought the Mk 48 down, and he said it took a couple days, but wasn't that hard.

  11. October 27, 2021Blackshoe said...

    Oh, a Danger Tag still up? That's it, your Tagout Program is UNSAT.


    The Mark 48 Shore Bombardment Computer seems to be the great-great grandfather of modern things like the DRT (and CADRT and DDRT).

  12. October 27, 2021bean said...

    The DRT dates back to this era, with the Mk 48 being a specialized use for this purpose. I think there's more detail in Network-Centric Warfare.

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