Your guide to the intercom system and radio channels on a B-17 as well as the related crew equipment. As always, please let me know if you have any follow up questions!
Some of my graphics come from this brief, but super helpful video on the intercoms of the B-17 Flying Fortress. I definitely recommend checking it out!
The interphone jack boxes are what was used to switch the radio channel an individual was listening to. There were eleven or twelve jack boxes mounted throughout the aircraft depending on the plane, one for each position.
Three were located in the nose for the navigator, bombardier, and forward gunner (like Bucky in ep 3)
Three were on the flight deck for the copilot, pilot, and top turret gunner
Two in the radio compartment, one for the radio operator and one for the Mickey operator/radar operator (PFF aircraft)
Three in the waist compartment for the waist gunners and ball turret gunner.
One in the tail for the tail gunner
These interphone jack boxes had five different switch positions, as follows:
The Compass Radio Receiver was a navigational instrument with a couple of different uses, though it had no transmission capability.
“The radio compass was used for aircraft navigation / homing: a beacon or broadcast transmitter could be tuned in, a loop antenna was rotated automatically to the transmitter direction and the result was displayed on the indicator.”
Here’s an excerpt from Crosby’s memoir, A Wing and a Prayer, that explains how the radio compass might be used by a navigator.
“Lead! I wasn't a lead navigator. On all my missions so far, I had been comfortable in a Tail-End Charlie plane. I could, more or less, keep track of where we were. On a practice mission, when engine trouble made Brady's crew drop out of formation and we had to come back alone, I found our way home. The radio beacon at our field, Splasher Six, was R5, read loud and clear, and with the radio compass I zeroed in on that.
But lead? If there were no clouds I could get to Liverpool, I could see the navigator's friend, a train track, the whole way, and when we got to the end of the railroad, Liverpool would be on the coast. On the northern leg of the flight I could follow the Scottish coastline all the way. On the way home I would tune in on Splasher Six, our base homing beacon, and let the radio compass get us back to the base.”
— A Wing and a Prayer by Harry Crosby
Going one step further, the radio compass could be used to cross reference the radio beacon schedules with the radio beacon bearings to triangulate an aircraft’s position.
The liaison channel was used to communicate with aircraft and with ground stations over large distances, upwards of 3000 miles depending on weather conditions and method of transmission. This would consist of things like reporting to HQ, receiving orders, providing confirmation of an attack, reporting recon results, etc. This would include receiving the code to recall the formation back to base.
Any crew position could listen to this channel, but only four jack box stations could transmit: the pilot, copilot, navigator, and radio operator.
Similar to the liaison channel, the command radio was used for short-range communication with other aircraft and with ground stations. This means on missions, planes would communicate to each other using this radio. This would usually include talking to control towers, issuing and receiving instructions from other aircraft in the squadron, etc. The reliable transmitting distance was approximately 25 miles, though with ideal weather conditions this distance was greater.
Note, usually fighter aircraft had only Command radio equipment. In Crosby’s book, he mentioned listening to their P-51 fighter escort talking to each and complaining that “the Berlin guys got all the action.”
Although any position could listen to the command channel, only the pilots and copilot had the transmission key. Meaning only they could make transmissions. The control box for the command radio was located on the ceiling of the cockpit, situated between the copilot and pilot.
I’ve included a section from Crosby’s memoir below to show how they interact over the different channels, specifically with the command, or in this case “task force,” channel.
I made a post a while back about callsigns used between aircraft and squadrons on missions. Feel free to check that out here.
The intercommunication system for use between crew members. Most flyboys kept their jack boxes on “INTER,” having no need to switch to any of the others. Unnecessary chatter was often kept to a minimum, but obviously there are exceptions when you throw ten young men in a tin can for eight hours straight.
Having multiple people talking over the intercom at the same time would cause issues, so they were instructed not to speak while someone else is using the system, unless it was very important.
A transmission channel that enabled the user to over-ride reception on all other jack box stations on the aircraft. A spring returned the selector switch back to "INTER" so that it cannot be left on “CALL” for extended periods of time. This was not commonly used as crews were told to avoid using it unless necessary.
Every crew member had a headset, and they were instructed to keep it on at all times. Their sheepskin flying helmets also had receivers built in, so they were able to switch to those once at the same time that they equipped their oxygen masks.
See the image at the top of the post for a labeled diagram of the typical headset and throat mic setup. The image below features two actors on set of Masters of the Air. You can see the microphone switch box and throat mic on Anthony Boyle who plays navigator Harry Crosby. Comparatively, David Shield, who pilot Everett Blakely, doesn’t have a microphone switch box because he is a pilot (see below for more info on this).
Their standard uniform caps, however, were often uncomfortable due to the grommet. Flyboys would remove the grommet so that the headset would sit properly on their head—a look that would be dubbed the “fifty mission crush,” alternatively called the “hundred mission crush.”
In the Air Force, a flyer wanted to be “hot.” He wanted to be able to handle his liquor and his women. When he got his picture taken, he wanted to look like a "rock," short for "hot rock." When a rock went into the air and put on his radio headset, the stiff top of his hat kept his headset from fitting close to his ears. So out came the stiff wire circular grommet. It never went back in, and the hat with the "hundred mission crush” was born. The more disreputable the hat, the better for the rock.
— A Wing and a Prayer by Harry Crosby
The throat microphone sensed and absorbed audio vibrations from the user’s throat. The oxygen masks would eventually become outfit with microphones as well, which made it easier when they were above 10,000 ft.
The microphone and radio headsets were kept on the aircraft at their stations, put on and cords connected once they were in position at their station.
You’ll likely never see them with their headsets outside of the plane. Crosby mentioned how he had forgotten to take off the headset from around his neck after one mission, so it is technically possible, but unlikely.
All microphone on the B-17 were push-to-talk, but not all of them had the switches on their person. The reason the flyboys would begin transmissions with things like “Navigator to pilots” or “Pilot to all crew” is because it was often difficult for them to distinguish voices, especially in the loud environment.
Speaking of background noise, according to multiple sources, the background noise on a B-17 varied from position to position. Those nearest to the propellers who have been exposed to more noise as opposed to those in the tail, or maybe even the nose of the aircraft.
The location of the intercom switches for each crew member were as follows:
Pilots had a button on their steering column that triggered their microphone.
The BTG had a switch on the side of the ball turret.
Top Turret Gunner/Flight Engineer
The flight engineer had a button on the handhold of the center column for the top turret.
The Navigators, Bombardiers, Radio Operators, Waist Gunners, and Tail Gunners all had a push-to-talk switch on a lanyard around their neck.
