November 29, 2022

U.S. Military Field Phones, by Ken in Michigan

If you are looking for a secure communication system for your farm, ranch, or retreat, then look into a military phone system. You can create an ideal communication system, any size, from two positions overnight to multiple positions in a large permanent retreat.

Military Field Phones (“MFPs”) do not require external power. They are designed to operate in adverse conditions and most importantly, do not emit any electronic signal. MFPs cannot be overheard by radio scanners or radio direction finders. MFPs keep your location undetected by electronic surveillance, unlike today’s radio communications that can be overheard and DF-located using today’s technology. Radios are also subject to interference, intentional or unintentional, friendly enemy or atmospheric. The only disadvantage in using a MFP is the requirement of the use of hard wire. A two-wire cable is used to connect the phones. This is “old-school,” otherwise known as POTS (plain old telephone system).

A little history is needed to fully understand the MFP: The first US MFP system was developed in 1910. In WW1, the EE3 phone was used with good success. In 1932, the MFP was improved and was standardized with the EE8 phone and the BD71 and BD72 switchboards connected using WD-1 wire, which aided in better communication. In the beginning of WW2, the EE8 phones had leather cases. The leather cases were replaced with a hard canvas case in 1944 (the leather did not hold up as well in the South Pacific during the Vietnam War; the canvas just rotted away). In 1967, the hard canvas case was replaced with a nylon case.

During the Vietnam War, the equipment improved with the TA-1 PT, TA-43 PT and TA-312 PT phones. The phones were connected with the SB-22 switchboard and had improved wire (WD-1A).

All of the MFP equipment is interchangeable and compatible. The 1930’s equipment can be used with all of the 1960 and 1970’s equipment. The plus is the MFP can be used with foreign nations phone equipment as well. I currently have four German phones in my inventory. I cannot personally guarantee that the Russia and Warsaw Pact’s will work with our simplex analog phone system.

Here are some of the basics of how the phone system works:

– Each phone contains a hand crank generator that produces 90-100 volts AC at approximately 20 Hz (which signals the receiving phone to answer the call). This generator is strictly for signaling and has nothing to do with voice communications.
– Communication is a “push to talk” button, just like any 2-way radio system. The system has a carbon microphone and uses 2 D-Cell batteries (referred to as BA-30 in the manual). The 2 D-Cell batteries give, in series, three volts of DC to amplify the voice communication.

The most basic system would be to connect two phones together. No switchboard necessary and polarity is not a problem. Several phones can be connected this way, but all phones would ring at the same time. It would be possible to work out a code: 1 crank to answer phone #1 and 2 cranks to answer phone #2, etc. There would be a limited number of phones to be connected this way. For most users, we would use a simple wiring system called the Platoon Hot Loop. This puts all the phones in a series, with no switchboard. Simply connect the first phone with the wire, pair one wire on each terminal on both terminals at the 2nd and any other intermediate phone (simply split the cable and only cut one wire). Terminate the two cut ends on the next phone leaving one wire uncut. The last phone is where you connect the two wires to the two terminals for connection, just like the first phone. This places all the phones in a loop in series. Polarity of the connection does not matter using this system. I found this in an article regarding TA-1 phones, but I do not see why it would not work on other field phones.

The next step up is to set up a SB-933/GT switchboard (Manual TM 11-5805-294-12). The switchboard is a small device weighing about 2 lbs. And consists of a terminal strip with moveable lighted plugs to connect to different lines. This system can be used for up to 7 phones and also requires an operator to answer the call and connect the call. The next larger system uses a SB-22 switchboard and weighs approximately 30 lbs. and can handle up to 12 lines. When a remote phone call is received, a buzzer alerts the operator of an incoming call. There is also a black flag on the incoming line that will flip white. The operator then plugs his phone cable into that line to connect with the caller. If the caller needs to communicate with another position, the operator can then connect to the desired phone line. In a common use situation, the switchboard would be in the headquarters requiring someone on duty at all times. The remote phone should be located at an observation post, defense position or sleeping quarters, etc.

The MFP’s range is listed at 14 miles in wet conditions and up to 22 miles under ideal conditions. There are various manuals with conflicting tables, so you may have different results. In the technical manual,TM-11-333, page 10 ranges varied from 11 to 100 miles for point-to-point systems, with different wire sizes. Communications can be used up to 360 miles with the use of overhead phone poles with open wires for point-to-point systems. A point-to-point system consists of batteries at each field phone and also at the switchboard. A switchboard-powered system consists of a power supply system at the switchboard and no batteries at the individual field phones. The range of this system is reduced by half the distance of a point-to-point system.

Another table shows range as 230 miles with a pair of #14 copper wires and 520 miles on a part of #12 copper wires. The switchboard power system must have the 3 volt DC for communication and a supply of 90 volt AC for signaling. This would be only be useful for extra large systems or to replace having to use D-cell batteries, at both the phone and switchboard. If you could limit a solar panel to 3 volt DC, that could work. Still use a hand crank for signaling to the phones. Switch the selector switch on the TA43/PT and TA312/PT phones from LB (local battery) to CB (common battery). There are several power supplies to provide this power either from 24 volt DC or 120/240 volt AC. For a 24 volt DC power source, use a PP-990/G power supply. For 120/240 volt AC, use the TA248 or 248A/TT power supplies. (Technical manual TM11-5805-304-14.)

Military phone wire is not a necessity. For the simplex analog phones referenced, they require a two (2) conductor cable. Any two (2) conductor cable will work as an extension wire, speaker wire or phone cord. It is even possible to use a single conductor with one terminal grounded at each phone. This will greatly reduce the range of communication. The military specification wire would still be best, it is designed for this use, if you can get enough.

JWR Adds: For permanent or semi-permanent installation at or between farms, ranches, or retreats, you can use any sturdy signal wire that is rated for underground (buried) use.

Common Simplex Analog Equipment:

– EE-8 phone (used from 1932 to the 1980’s); 2 D-cell batteries required; total weight
approximately 10 lbs. Technical Manual TM-11-333
– TA-43/PT a much more compact phone with a canvas case and hand set; buzzer volume control;
2 D-cell batteries required; total weight approximately 9 lbs. Technical Manual
TM-11-5805-256-13
– TA-312/PT almost the same as the TA-43/pt but now has a receptacle to accept a H-144 headset
instead of a handset; 2 D-cell batteries required and total weight approximately 9 lbs. Technical Manual TM-11-5805-201-13
– Additional manuals:
TM11-5805-201-23P (Parts Manual) TM11-5805-201-12 (Operator Manual) TM11-5805-201-35 (Maintenance Manual)
– TA-1PT a compact phone, totally within the handset. It has a buzzer control volume that can be turned off when needed and has a black and white spinning disc to notify of incoming calls. No batteries required, but range is reduced from 3-4 miles. Comes with a hard plastic holster and canvas bag to be worn on your belt or carried in your pocket. Technical Manual TM11-5805-243-13, approximately 3.5 lbs.
*Additional manual: TM11-5805-243-23P (parts).
Optional Amplifier: TA-287/G. This will add 24 miles to the range of any single phone.
Switchboards:
– SB-993/GT is a simple mini switchboard that can handle 7 lines, no batteries required.
– BD71, WW2 and Korea era. It is a wooded case with folding legs, handles 6 lines and requires
batteries.
– BD72, WW2 and Korea era. This is the same as the BD71, but handles 12 lines.
– SB-22/PT Vietnam era. This is a 12 line switchboard with an aluminum case and is more
compact and durable than the earlier wooden cased switchboard systems. This switchboard weighs 30 lbs. And two can be stacked together to create a total capacity of 29 lines, when assembled with an accessory cord pack.
Technical Manual TM11-5805-262-12 (Operational Manual) Technical ManualTM-5805-262-35 (Field and Maintenance Manual)
– SB-86/P is a 30 line, expandable to 60 lines, 180 lb switchboard with a watertight case. This system is beyond most of our needs. This is used at brigade level to communicate with battalions.

While I have been listing manuals, one good one for the larger system is FM24-20, Field Wire and Cable Techniques. This manual covers running phone wires and splicing. It also lists other equipment to put larger systems together. This manual makes it easier to understand how systems work together.

Wire (most commonly used): Early wire was a twisted pair of 22 gauge copper wire with rubber and cotton insulation. The most common wire we see today is WD-1A/TT, which consists of 2 conductors of 20 gauge wire. Four of the seven strands are copper and the remaining three strands are steel. This gives the wire a 200 lb pound tensile strength with a black nylon extruded jacket. This weighs 48 lbs. per mile. A second common surplus wire is WF 16/U, consisting of a red/green twisted pair of wires. This weighs 62 lbs. per mile.

Wire Reels:
– The most common (and handiest) wire reel is the DR-8 (9” diameter x 8 1⁄4” wide). It holds 1⁄4 mile
(1,320 ft) of WD-1/TT wire and weighs 12 lbs. It has a 2 post terminal strip (M-221 connector) with the inner end of the wire connected to it. It will hold more of the thinner WD-1A/TT wire and up to a mile (5,280 ft) of WD-36/TT wire that comes in canvas donuts. The purpose of the terminal strip on the reel allows you to unreel only the amount of wire needed without cutting wire off. Connect the phone to the terminal strip and re-reel wire when done. There is a hand cranked dispenser and can be unreeled with one hand or can be mounted on a backpack frame or shoulder straps to rewind. This is a RL-39.
– The next larger reel is the RL-159 (19 1/4” diameter x 7” wide) that holds two kilometers (6,562 ft) of WD-1A/TT wire. This reel has a square 1” hole to mount on a hand or machine-driven reel machine. The largest reel (for our use) is a DR-5 (19 1⁄4” diameter x 18” wide) that holds 2 1⁄2 miles of WD-1A/TT wire (120 lbs of wire). This goes on a vehicle. You will need a braking system to stop or slow its spin. If you allow a reel to over-spin, you are going to have a big mess. Imagine a giant fishing reel full of backlash (or a birds nest).

– The one wire we haven’t talked much about is the WD-36TT (assault wire), a 2 conductor 22 gauge aluminum wire cable (9 lbs per mile, tensile 25 lbs). Black nylon jacket that comes in canvas donuts (cannot be put back in donut). Original Vietnam era canvas donut MX-306A/G, 1⁄2 mile of WD-1/TT (2,640 ft) weighing 23 lbs, 13” diameter x 6 1⁄2 deep (obsolete by 1967).
– The same MX-306A/G (1⁄2 mile) was upgraded to the WD-1A/TT and was produced until about 1995. More current and available are the MX-6895/TT (2 1⁄4 lbs for 1⁄4 mile) and the MX-6894/TT (4 1⁄4 lbs for 1⁄2 mile).

General rule for Donut Wire: Do not prewire — use only when needed. One person can carry four 1⁄4 mile donuts, dispense while walking, splice together as needed (9 lbs per one mile). When done with this wire, roll it up on an empty DR8 reel.

Reel Winding Tools:
– We mentioned the RL-39 for the smallest reel, DR-8. For the RL-159 reel use a RL-31E.
Basically, a folding sawhorse that can handle (2) RL-195 or (1) DR-5. This has a crank handle
and a manual brake.
– A power reel machine for RL-159 reel mounts on a Jeep or other vehicle and is run by a 24V DC
motor. It’s A RL-172, weighing 100 lbs (TM11-3895-207-14). The reel machine for the DR-5 reel is gas engine driven, it is a RL-207 (weight 500 lbs) [a pipe across a stepladder will work too!].

All of the simplex analog equipment mentioned above will work with each other from WW1, WW2, Korea and Vietnam. The more modern military phone equipment goes digital and is requiring a 4 wire cable. This allows direct dial from phone-to-phone and eliminates the need for a switchboard operator. The most common digital phone system I have seen available is the TA-838/TT and SB-4170/TT switchboard. There is a tone signaling adapter to put on the SB22/PT switchboard to connect to some digital phones. I have not worked on digital phone systems, so I will leave that to someone else. I hope that what I wrote will allow others to understand the MPF systems.

In SurvivalBlog, published on October 21, 2006, JWR mentioned the AN/TA-1042 (direct dial phones that use 5.5 – 28 volt DC) that require a 4 wire cable. AN/TTC-39D tactical switch will also be necessary. He reported good results communicating with those duplex digital phones. They will not be compatible with the older simplex analog phone systems without additional interface equipment. Another duplex digital system available consists of TA 838/TT phones and a SB 4170/TT switchboard.

Finding the parts: My major source for finding equipment has been at the MVPA meets (Military Vehicle Preservation Association). Members and Vendors bring tons of items to the shows. Flea markets, gun shows and military surplus dealers are also a good source of these supplies.

Suppliers that have been helpful

Portrayal Press

Pat Tipson
Pat supplies reprinted manuals for military vehicle collectors and has most manuals mentioned.

VTS Industrial
www.phonesurplus.com
Steve Hilsz, Salons, AZ
520-370-3267
Steve collects and rebuilds Korea era and older phones.

Signal Center
[email protected]
Pete Martinez, Major US Army, Retired Signal Corps, Vietnam Veteran, Texas
Pete rebuilds and sells Vietnam-era phone equipment.

There are several other devices that can be added to the basic MFP system, such as the telegraph teletypewriters, etc., but one system that seems most useful is the Remote Radio Controllers that allow a phone operator to remotely operate a radio. In use, the remote radio must be turned on and channel selected. The remote unit can listen to the radio, key mic to talk. The local unit at the radio has a cord to plug into the radio mic jack on military radios. There is no reason you couldn’t make a patchcord to fit any commercial radio! A radio with its own power supply can be placed on a hilltop or tower and be operated up to 2 miles away over standard phone wire. This has the added benefit of the radio being located by direction-finder and will not give the operators position away. Some of these systems are RC-290 (1950’s era), and later units consisting of the AN/GRA-39, which consists of two units C2328 remote and C2329 local (TM11-5820-477-12). Each unit requires 6 D-cell batteries (12 batteries total). This was upgraded to HYX-57. The HYX-57 needs two units, which are interchangeable. A lot of information on the military radio systems is posted by Brooke Clark, www.prc68.com. He also makes battery adapters for using common batteries instead of obsolete military batteries.

The single most troublesome problem I have had with MFP is due to age. The microphones are filled with carbon powder and can clump up with time. All you generally need to do is take the mike out of the handset and tap it on the edge, roll it around, then roll it down the stairs. It may work. Replacements are still available. There are a lot more old civilian phones around than military ones. A friend just sent me two Western Union mics (Model #???). They fit the TA-1 perfectly, but have not tested them yet. Hopefully, there are other people out there that can add additional information to the comparable replacements. The rubber gets brittle in the rubber coil cords and connections may need to be replaced. Never store the phones with the batteries in them. In use, the batteries last a long time. They are only used momentarily when in the “push to talk” position. I would buy the best long life batteries and place them in a plastic baggie with your phone.

I believe the simplex analog MFP should be immune from EMP when disconnected from any wires. There are no electronics to be fried by the E1 EMP wave. I still store mine in an EMP proof box for safety. If they are connected to the wires at the moment of an EMP blast, they will get fried by the E2 and E3 waves, just like any other electrical equipment (generators, buildings, well pumps, etc.).
I hope this article helps others understand the military field phone systems and what is available and how to recognize what you are looking at. We can keep it simple or build as complex of a system as you would like. Looking forward to any feedback from those more knowledgeable.

Good luck to all.

Sources: All of the military manuals I could find and articles posted in military vehicle web sites such as Steel Soldiers and Olive Drab.

Disclaimer: I do not receive any benefit from MFP sales nor do I receive anything from the vendors mentioned.

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