USN WWII AA Fire Coordination

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Hummer Mole

Apr 27, 2007
Gents, looking some pretty specific info I've been unable to find anywhere else. I'm doing some research on US Navy Carrier Task Force air defense during the Pacific campaign and need some info on how US Navy ships directed coordinated their light AA guns. I have a lot of info on the 5"/38 and Mk37 Director, and have done some research into the Mk51 director for the 40mm Bofors gun. From what I've been able to determine, most of the 40mm guns used the Mk51 director. I've seen reports that 20mm Oerlikons were sometimes also slaved to the Mk51 director, although I've yet to see a 20mm mount with the drive and control gear necessary for automatic director control. My main question is what type of coordination was used for the manual 20mm and .50 caliber mounts? In some wartime pictures of the light gun batteries, I've seen pics of guys with headphones standing behind a group of single mount gunners. I can only guess they're talking on one of the battle interphone circuits to the CIC to get the general direction of approaching aircraft, or get targeting priority. Anybody have any more specific information or vectors in the right direction?


Hi Glenn,

I suppose You already have:
Mark 51 FCS
and relating to the synchro device:
Selsyn and Synchro Devices

As far as what I understand the USN and USAF tended to use amplydines (a sort of self exciting motor generator with postive feed back) to provide the power
for pointing guns, altough I have no idea if this relates to the 20mm also (I doubt this).
The revolutionary step of AA FC was made with the US MK 37 FC. Will see if I can find more.

kind regards,
I think both the 20mm and .50 were hand operated and not slaved. Never seen them slaved. Same with the newer 25mm. It was an eyes on operation.

Trained with the .50 and directing was never noted. There was a loader, gunner arraingement. The guy with the phones is most likely linked to CIC (as you guessed) getting called on which threat was the target and from where it was coming. For the guys on the hand operated mounts back in WW2, the report would either come from the talker (guy with the headset) or over the 1MC (shipboard PA system). Something like " Air action Port Quarter" or "Surface action Staboard Beam". It told everyone on the hand held weapons where to look and what to shoot at.

There were also several conditions for the gunners:
Situation White- (No threats)
Situation Yellow- (Threats possible)
Situation Red, Weapons Tight- (Threat imminent but weapons on hold due to friendlies in area or other circumstances)
Situation Red, Weapons Free- (Have at it, everybody out there is a bad guy)

PS- All this is general as I may be confusing 1980s operating standards on a Gearing with 1940s operating standards for the same ship.
Tim - good info. I'm trying to nail down some specifics about what you're referring to - what interphone circuit and who was on it, etc. Thanks for the gouge. Weapons free - we probably won't hear that ever again in the USN.
Can't remember the circuits. If you go to any WW2 ship museam, you can see the circuits throughout the ship. If you make it up to Combat (CIC), you'll see them all over the place. Usually, you screwed a sound powered phone into it and turned the switch to whichever circuit you were supposed to be on. I think there was Engineering, Damage Control, Lookouts, Fire Control to name a few. Usually, there were half a dozen at least on each circuit during GQ. No bs-ing around on the circuit, get on and get off. But sometimes, when you knew everyone on the circuit, it was "What's up on your end of the ship?" type of talk.

As for Situation Red; Weapons Free, it will happen some day. Probably for some of those smaller ships in the Brown Water navy, it happens now. But for the bigger ones, it might be a bit different. Now, if they empty their magazines at all the threats, they're empty in a couple minutes. Weapons have a much higher % of hits.

But it will happen. Sooner or later.

Glad I could help.

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