Need manuals/schematic for Sperry K4 gunsight for lower turret ball gunner in B17

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Bill Akins

Jul 8, 2006
I have a lower ball turret automatic computing gunsight from a B17
bomber in very good condition. I acquired it from a cousin of mine.
The plate on the gunsight reads..."Automatic computing sight for
turret (lower ball) type K4 Sperry gyroscope company Inc."

I removed the bulb cover and bulb from the back of the sight and shone
a flashlight into the opening. I was able to see the sight reticle
reflected onto the reflector glass and able to spread the reticle
lines by turning the "target dimension feet" knob. Probably the first
time anyone has looked at the reticle shone onto the reflective glass
in this sight since WW2.

The gunsight is very well sealed with all wire route openings capped
with yellowed plastic caps. So no debri, bugs, etc have entered the
gunsight. She is sealed as good as the day she was first sealed and
put into storage. I did a bit of research yesterday
online to try and find out more about this sight. What I need is any info
there might be on this gunsight.

I need an operators manual as well as a technical repair manual as well as a
wiring schematic on this Sperry K4 lower ball turret gunsight. So far I have been unable to locate
these WW2 manuals/schematics online or otherwise. To get the sight
operational I must find and acquire these.

I have been able to find out that the belly turret gunner used a left
foot pedal which he depressed and then released, to bracket in his
reticle the wingspan of an attacking fighter. Then he adjusted the
"target dimension feet" knob to bracket the wingspan as well. There is
also a mostly covered knob labled "range 100yds" and this knob has a
small opening in its cover and I don't seem to be able to turn it.
Not sure exactly how that knob figures in yet either, but I think it
might be a knob that you unscrew the cover and set for different
ranges, then screw the cover back on. Need a manual! Mine is the type
K4 which was only used on B17's and B24 bomber belly turrets. The K3
is an identical sight but was used on the top turrets. Mine is the
same gunsight just turned upside down from the K3 and the printed
lettering on the knobs and switch instructions is also upside down
from the K3 top turret gunsight. Again, any Sperry K4 gunsight info on
technical and operation manuals and a wiring schematic would be
greatly appreciated.
Send any info you have to me at [email protected]

Here some text and websites with photos regarding the Sperry K3 and K4
bomber self computing gunsights.
At this website you can see my K4 gunsight hanging upside down in the
pic of the belly turret's interior
Sperry Ball Turret

At this next website someone gives a very good description of how the
gunsight operated. ball turret ops

AT this next website you may enjoy reading about and seeing pics and
drawings of several different types of gun turrets, but for my Sperry
K4 belly gunner sight specifically, scroll down until you see the
drawing of the ball turret and gunner facing you with the caption
above the drawing reading..."The Briggs-Sperry Model A2 ball turret.
This drawing shows the ammunition storage system, suspension ring and
gunner's field of view." Then read the text below that drawing until
you see... "The Sperry K4 sight was then checked..." and that is
talking about my gunsight. Here's the link.
Axis History Forum :: View topic - US Aircraft Gun Turrets in RAF Service

This next website has quite a bit of info on the Sperry turrets and
gunsights. It also lists a location for some turret manuals and
reprints of manuals that cost inordinate amounts. Thus far this is the
ONLY place I have found mention of manuals, but these are for the
Sperry turrets themselves and are NOT the manuals and schematics for
the Sperry K4 gunsights, so I don't need turret manuals. I need
manuals/schematics for the K4 gunsight itself, not the rotating
turret. Here's the link.
B-17 top turret project

This last link is from our own site here and is about B29 gunsights and info, but it did
include this below text about the Sperry K4 gunsights used on the B17
and B24..."Incidentally there were computing sight in turrets going
into WWII. The B-17 and B-24 has computing sights in their upper and
ball turrets. The K-3 sight was used in the upper turret of the B-17
and the K-4 was used in the lower ball turret. These sights were
similar in their computations or range and deflection but they didn't
take temperature and acceleration into account. These sights didn't
use selsyns for position nor did they need to calculate parallax as
they were mounted inside the turret in front of the gunner. He would
manually input wingspan and range information and the sight would
adjust the gun sight. The gunner would keep the sight on the target
and adjust the range, typically with a range foot pedal. The sight was
connected with flexible shafts to the azimuth and elevation gear boxes
to receive position information. They even came out with compensating
sights for the single waste guns in the B-17, B-24 and the B-25. These
sights were also connected to the gun mount with flexible shafts to
give them azimuth and elevation inputs."
Here's the link to that above text ......

I gave you a lot to read and if you read it all I hope you come away
with a new appreciation of WW2 bomber turrets and their gunsights.

Please help me find the operational, maintainance and repair
manuals, and wiring schematic for my Sperry K4 belly turret gunsight
so I can get it operational for future generations to enjoy.

Thanks for taking time to read all this, I know it was a lot.

Bill Akins
Member of the board of directors of the Florida Aviation Historical Society.
F.A.H.S. Website... FAHS_Website : Florida Aviation Historical Society

Director of the Sunken Warbird Recovery Team.
W.R.T. website... The_Warbird_Recovery_Team : The Warbird Recovery Team
Hi Bill, Try giving Greg Rainone aka Pike Bishop <[email protected]> an email. He makes and sells copies of manuals on ebay and I've bought a couple from him. He's had a couple dealing with the Sperry sight previously although none right now. He might make some fresh for you. On ebay he goes by


his info is

Greg Rainone
P.O.Box 189Arlington, TX 76004
United States(817)461-4867

Bill Bogdan
Hi, Bill

The best place that I know is to contact the EAA's (Experimental Aircraft Association) Museum. They own and operatate the B-17G Aluminum Cloud that they put on tour every year. Actually in the museum they have a complete B-17 manual that you can look at or is it a B-24. Any way Im pretty sure that the library there would be able to help you or be able to point you in the right way. Below is the link to the library.

EAA's Boeing Aeronautical Library

Hope that helps.

Bill, I'm doing research on the ball as well, for a 3D modelling project. You have better links than I have, but I did want to comment on the range dial. In photos I've seen, there is a cable between the range pedal and sight (of course for the reticule). I think the cable also causes the range x 100yds dial to show the numerical value of your foot position. I would think it's position doesn't make it a primary means of sighting, but it probably provides "confirmation" of the range you estimated when closing the sight ring to the wingspan. Maybe it helped a gunner "train" his foot or possibly allow him to "catalogue" a pattern of fighter attack.

By the way, you cleared up a lot of things for me (e.g., I thought pictures were showing 100 yards on the dial cap, but now I know).
By the way Bill, does your sight have the backup sight mounted behind the optical sight? If it does, I was wondering if it could be rotated out of the way when not in use.
By the way Bill, does your sight have the backup sight mounted behind the optical sight? If it does, I was wondering if it could be rotated out of the way when not in use.

Thanks to all for the helpful info.

Yes Buster_Dee, my sight does have the backup sight and it does rotate out of the way.

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