Notes on Military Radios & Procedure
You're doing it wrong. And "you" includes most of the people who write scripts for TV shows, even movies, as well as those who write fanfic. A lot of people are doing it wrong.
Now, in Hogan's Heroes fandom, canon gets a disturbing number of things very badly wrong. The airplane in "Hogan Gives a Birthday Party" for example: the stock footage they used shows at least two different planes, neither of them anything close to what the plane is said to be. Or the "tank" in "Hold That Tiger" – they didn't even bother to try to make that self-propelled howitzer look anything like a Tiger tank, or evan a tank at all. So, yeah, there's a precedent for getting things wrong, and badly wrong. But that's no reason for us fanfic writers to not get it right.
So, a few comments on military radio procedure and radios. A little online research will supply an embarassment of riches, but here's enough to keep your stories from being glaringly incorrect.
First of all, forget everything you ever learned about civilian CB radio, especially if you learned it from the movies. Military procedure doesn't work that way. For that matter, CB procedure didn't work that way. Just forget it entirely.
Very specific terminology is used in radio communications for the sake of clarity and brevity. This is particularly important if people accustomed to different native languages (as in this case) are involved. It's essential that the person receiving a message be able to understand exactly what was meant. All else aside, having to ask for clarification takes time. Radio channels are like party lines, not private phone calls, and it's important to clear the channel as quickly as possible because other traffic may be waiting. And, of course, you never know when hostiles may be listening, including hostiles with RDF gear. Plus it's generally a noisy environment, not just on both ends but on the radio link as well. So specific words with specific meanings are used. That's where writers seem to run into problems.
The phrase Over and out is simply wrong. Period. End of sentence. This is probably the most common error, especially in canon – common to the point of people thinking it's right (and the cause of a lot of push-ups among novice military radio operators for that reason). "Over" means "you talk now, and I'll listen" while "out" means "I'm signing off and going away." It's one or the other. You can't be both listening and going away at the same time.
Roger and wilco do not mean the same thing. The former means "I understand what you said"; the latter means "I will comply".
Repeat does not mean "transmit your last message again;" it means "drop another artillery shell where you put the last one." When you hear someone in everyday life respond to a half-heard statement with "say again?" the odds are they're former miliary. If Hogan is asking London for something strange, London would reply with "Say again, Papa Bear?"
Affirmative and negative are used in place of "yes" and "no" because they are easier to distinguish in a noisy channel.
Anything that needs to be spelled out uses the phonetic alphabet. Well, uses a phonetic alphabet; precisely which one, pre-NATO, could be complicated. For general HH fanfic use, the US Joint Military alphabet should suffice. It's the first option in the converter here on Hero Files.
First of all, although canon has a lot of voice communication for dramatic purposes, in real life it would be mostly or entirely Morse code, aka CW. For one thing, the majority of communications were AM, and AM radio, especially with the technology of that era, is extremely noisy. Clicks are much clearer than words. For another, Morse requires much less power to communicate. This is particularly important to the operator of a clandestine station, which would be pretty much everyone in our scenerios except London. A good Morse operator can send and recieve almost as fast as someone can talk, and in a noisy environment, not having to repeat messages more than makes up for any loss of speed.
What this means to us as fanfic writers is that radio operations is a specialty, and a critical one. Kinchloe and Baker can do something very important that most of the people in camp can't, and even though they've probably taught some of the others, they're still going to be much faster at it. Joe Schmoe, even Private Joe Schmoe, can't just pick up a microphone and have a chat with London. This can set up some interesting situations for fiction.
Radios of the era were not small things. For one thing, most of them (crystal or "foxhole" radios aside) used vacuum tubes. Now, tubes are big. The average audio tube would be big enough to put one of today's MP3 players inside. They're also fragile. Aside from the whole glass envelope issue, they work loose in their sockets. Their internal elements can break. For those not familiar with tubes, imagine a really complicated incandescent light bulb. Now put a half-dozen or so of those into a radio. This is not a rugged instrument.
What is commonly but erroneously called a "Walkie-Talkie" (that name actually referred to a backpack-carried radio) was the SCR-536 Handie-Talkie. It was not a small device. It was over a foot long and three inches square, and weighed over five pounds. It was crystal-controlled, so it had one fixed frequency; changing to a new crystal for a different frequency required recalibrating the radio, which took time and the proper equipment.
A handheld radio was a great thing, producing enormous tactical advantages. However, it was not something that one could slip in one's pocket like a modern two-way radio. The range limitation would be a major problem for communication between a team in the field and a radio operator in the tunnels. For coordination between two field groups, the handheld radios would be a huge advantage. But for routine communications in clandestine work, their drawbacks (not least of which is their obvious Allied origin) would overcome their benefits. They also depended on batteries that, in the HH operation, could not be easily replaced. The batteries would probably have to be dropped in by London, with all the risk that entailed, though I wouldn't put it past Carter to build some given information on the proper chemical mix. The batteries did not have a long life, either. Remember, you're feeding tubes here, and tubes need a lot of power just to get to operating temperature; the filament has to get white hot. Battery technology of the time was primitive by our standards.
In short, if you imagine a child's toy walkie-talkie in a case the size of your forearm, and with the ruggedness of a box of light bulbs, you have a Handie-Talkie.
Receiving is always easier than transmitting. You can make a radio receiver, including a crude detector, out of household items. Many POW camp radios of that sort were made. It's highly likely that most members of the (already fictional) Underground would have receivers only. They could be told when and where to meet, for instance, but they would be unable to reply.
While London would always have someone on radio watch, it's unlikely that the Heroes would be able to do so, and borderline impossible for any Underground contacts. There would be regularly-scheduled contact times set up, and if a message was to be transmitted, it would be during one of those times. Again, this is something that can be used to add tension to a story. It's also a reason to send a messenger or use other means of communication if the scheduled radio contact won't take place in time. This is particularly true of the S-Phone and Joan/Eleanor communications systems used by agents in enemy territory, like our Heroes. They could have excellent communications by way of high-flying aircraft, but only at the specific times those aircraft were scheduled to be overhead.