US AFV Radio Equipment in WWII


Picture 1:
US radios used in AFVs in WWII were based on the transmitter/receiver component design utilized by most countries in the late 1930s. The major difference was that the Americans used mostly FM wave bands (frequency modulation), instead of AM (amplitude modulation), for their voice communications. FM signals, although of limited range when using the weak power supplies of the time, produced a clearer broadcast quality with reduced static noise from the engine and other electrical components in the AFV. This was a great advantage over AM signals, and combined with their advanced radio technology and manufacturing, US radios were generally of superior quality and were built in great quantities during the war. This web page is a revision of the original that appeared in AFV INTERIORS in 1997.

There were a number of radio sets developed by the US Army Signal Corps in the late 1930s and 1940s, each designated by the letters SCR (Signal Corps Radio) and a three digit number. Each radio set could have a combination of transmitters, receivers, power supplies, and accessories, and the choice of which set would be used for a particular vehicle depended on the level of command communication necessary. Luckily, there were only four sets that were found most often in US combat AFVs during the war. Although typically there was only one transmitter mounted in each vehicle (except in command AFVs), the number of receivers a vehicle contained depended on how many different radio nets the users had to listen in on. These four basic radio sets are outlined below.

COMMON RADIO SETS USED IN US WWII AFVs

Radio Set

Components/Description
SCR 538 FM/voice only, 10 miles max, no transmitter, 1 BC 603 receiver w/ BC 605 interphone amplifier, 9' whip antenna, typical tank set in early war years
SCR 528 FM/voice only, 10 miles max, BC 604 transmitter (20 Watts, 10 crystal channels, 8 tubes) w/BC 605 interphone, BC 603 receiver, 9' whip antenna, platoon leader and typical late-war tank set
SCR 508 FM/voice only, 10 miles max, BC 604 transmitter w/ BC 605 interphone, 2 BC 603 receivers, 9' whip antenna, tank company commander
SCR 506 AM/25-50 miles voice, 75-100 miles key, BC 653 transmitter (50 Watts, 4 tubes), BC 652 receiver, BC 658 interphone switch box, 15' whip antenna, battalion commander, when 506 was not avail, older SCR 245 or SCR 193 w/ less range was used

In order to communicate with nearby ground troops outside the AFV, tankers often used an AN/VRC 3 set (which was a modified SCR 300 wireless walkie-talkie pack-type radio) mounted inside the turret. Although of short range, it did provide necessary voice communication for coordination and control between AFVs and accompanying infantry.

There was also a BC 1362 or RC 298 intercom extension kit with an external phone box mounted on the rear of some vehicles, again meant for communication between infantry at the rear of the tank and the vehicle crew inside. The outside components consisted of a wired handset in a weather resistant armored box, and its use by ground troops outside would light up a flashing signal light in the turret of the tank to notify the crew.

If you are attempting to determine the location of a radio set within an AFV, keep in mind that the electrical slip ring assembly-- the rotating electrical connection between the hull and turret-- was a fairly primitive design during WWII. Therefore, the radio set was located in close proximity to the outside whip antenna so wiring through the electrical slip ring was not necessary. So, an antenna mounted on the turret indicates the radio set was also mounted in the turret; an antenna mounted on the hull indicates the radio set was mounted in the hull. Although most US tanks in the first year of the war had their radio down in the hull (M3 Stuarts, for example), by 1942 most radio sets were mounted in the turret, British style. An exception to this rule were tanks that contained command SCR 506 sets which were typically mounted on the right side hull sponson, using a separate 15' whip aerial that was mounted near that location on the hull. Of course, open topped vehicles, such as M10 tank destroyers, often did not have room up in the turret for the radio, and their radios were mounted down in the hull, usually operated by the assistant driver.

Below is a short synopsis of US AFVs and their most common radios:

MEDIUM TANKS

AFV

Radio Set/Comments
M3 (US Lee) SCR 508, or 528, or 538, mounted on sponson to left of driver
M4 Same radios but mounted in turret bustle, w/ second command radio possible in rt. front sponson
M26 Same as above

LIGHT TANKS

AFV

Radio Set/Comments
M2A1 SCR 193, SCR 209, or SCR 210 on rear fighting compartment wall. No interphone.
Combat Car M1/M1A1 Same as above
M3 SCR 210 rt. spons, SCR 245 (comd.) left spons., interphone RC 61
M5 SCR 508, 528, or 538 in left spons. (in turret bustle in M5A1), SCR 506 (comd.) in rt. spons.
M24 Same as above but in tur. bust., SCR 506 (comd.) in front of ass't. driver

HALF TRACKS

AFV

Radio Set/Comments
M2/3 SCR 499 and SCR 542, or 14 other possible combinations

Picture 1:
So let's take a look at each of these four radio sets and see how they were similar and differed. This is the SCR 538, the basic tank radio set used during the first years of WWII, here seen mounted in the turret bustle of a M4 Sherman tank with 105mm howitzer. It consists only of the BC 603 receiver (at right with the speaker) and the 605 interphone amplifier unit. Notice the American design use of push-button controls on the far right of the receiver and the built-in speaker, indicative of many US radios. The typical radio mount in WWII US AFVs was a special metal shelf, FT-237, which was specially designed to mount any number of radio sets securely by the use of knurled thumb nuts along the front edge of the shelf. The SCR 538 was generally replaced with a set with a transmitter (SCR 528) as the war progressed for battle tanks on the front lines.


Picture 2:
Here is a photo of the turret installation of the BC 604 transmitter and a BC 603 receiver (at right) combination that made up a SCR 528 set. The transmitter utilized a built-in interphone for internal communications and is characterized by the large plain box with a row of push buttons along the right side under a meter dial. The BC-603 receiver worked from 20 to 28mHz, utilized a continuous thumb wheel tuning system plus 10 presets push-buttons, included squelch and a built-in speaker. Radio connection wiring attached to the back of the units and in this case the antenna lead snakes up the right turret wall (at left) and up to the roof where the antenna would be mounted. The shelf mount is the common FT-237; the SCR 528 set was typically used by platoon leaders early in the war and became the typical radio set for all tanks by mid-war.


Picture 3:
This photo illustrates a SCR 508 set installed in the bustle of a M24 Chaffee. Again, there is a BC 604 transmitter with RC 298 interphone on the left and to the right are now 2 BC 603 receivers, one for the company internal net and one for battalion net. There were 10 different channels (crystals) available by pushbutton for the voice radios along with the capability of 100 different channels by changing crystals. As each company had its own assigned channel, a divisional commander could listen in, or communicate, with each company with a radio tuned to each company channel. This is the view looking down through the large open turret roof door. Vehicles with this radio onboard generally belonged to company commanders or higher ranks. Many companies/divisions had a policy of mounting an extra dummy antenna on all their tanks, as the company commander's tank with two antenna (2 BC 603 receivers) often received the first shots from the enemy during an ambush situation.


Picture 4:
The last of our four radio sets is the SCR 506 which also appears in command tracks. It was composed of the BC 653 transmitter (50 Watts/4 tubes), BC 652 receiver (11 tubes), and a BC 658 interphone switch box. As I mentioned earlier, the SCR 506 was an AM unit and was used for long distance contacts, up to 100 miles with the Morse key. This one is mounted in a T41E1, which was a command version of the M39. To the far right are two power units, one stacked on top of the other, and the large set in the center has a large channel vs. frequency plate attached. Hanging off a hook to the right are connectors for microphones and a head set.

Typically, the SCR 506 was mounted in the front right hull of a unit commander's tank and was operated by the assistant driver/hull machine gunner. All US radios contained delicate vacuum tubes that would die at what seemed the worst times. Vacuum tubes, also known as valves, are what receives the radio signals and amplifies them so they can be heard. In US vehicles in WWII, AFV crews were generally required to carry a complete set of replacement tubes. Most units were taught to replace all the tubes at once if one should fail because it was too difficult and time consuming in combat to search for the one tube that had gone bad.


Picture 5:
The US communications gear worn by tankers early in WWII is illustrated in this well-known, but seldom identified, photo of Sergeant Childres of the 2nd Armored Division (Hell on Wheels). The crash helmet is similar to period padded football gear and contains pockets over the ears for thin earphones. Around his neck is a dual throat microphone with connectors to the small black interphone box on his chest. A small switch on the interphone box allowed the Sergeant to switch back and forth between his crew via interphone, or to other vehicles via the radio system. Unfortunately, leaving the switch in the wrong position sometimes led to tank commanders saying some pretty nasty stuff over the company channel when they forgot to switch back to interphone ("Damit, Jones, I've been telling you for the last five minutes to turn left, what the Hell are you doing down there....").

The leather crash helmet/headphone set-up was uncomfortable and unpopular with crews, and by 1944 a cushioned set of headphones was generally worn under the outer steel pot of their combat helmets when in the front lines. Tank commanders often used a handheld microphone that provided clearer voice communication than the throat microphones (see picture, top of page). The microphone was supplied with a very long cord allowing it to be passed outside the vehicle.


Picture 6:
Here is a US Army photo of the hull machine gunner/radio operator in a M10 tank destroyer during training in England. The radio is mounted on the right sponson to his right (no room in the turret bustle) and his right hand is holding the interphone control box hanging from a cord around his neck. You can imagine the limited view afforded by the M4 periscope when all closed down like this. US radio sets, like early Model T automobiles, came in any color as long as it was black. On rare occasion the boxes would be painted a shade of green. The interphone control was also black and the helmet was a natural brown leather color. Most US AFV's interiors were mainly white and in this case the periscope body is dark gray with the bottom prism container black.

Finding reference information about WWII US armored vehicle radios can be very difficult. But for technical information on radio sets and components, see the US Signal Corps Museum web site. If you have anything further that you might like to add about this subject, we would be happy to hear from you. All photographs are from US Army vehicle technical manuals or from the US Army photo archives.


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