Monday 18 September 2023

Copper Horns

The need for communications equipment in armoured vehicles became clear soon after their creation. Semaphores and signal flags were just a half measure. It was necessary to equip tanks with radios, but the road to equipping even a part of them was a long one. The modern system with a radio in the turret and a whip antenna was also far from the initial norm. There were many alternative visions of how a tank radio antenna should look.

The rail antenna was a characteristic feature of Soviet tanks in the 1930s.
Rail antennas became one of the characteristic features of Soviet tanks in the interwar years. "Horns" around the turret became a calling card of this generation of tanks. Few people stop to consider where such a strange antenna came from and how it works, especially since their age was brief. They were no longer used by Soviet industry after 1939, as opposed to the nation that came up with them originally.

A present from the Germans

The Red Army began to think about placing radios into tanks in the late 1920s. Initially, things were not going well. There were some experiments, but no mass production. There was no shortage of ambitions, as MS-1 tanks from the third and fourth production batch came with a large rear bustle. The bustle was also supposed to hold an antenna with the evocative name of "tank mushroom". However, the MS-1 did not get a radio in production. To be fair, most tanks of the 1920s were just as "deaf".  

Rail antenna of the Grosstraktor tank. This design migrated to the Pz.Bef.Wg. in a slightly different form.

Frequently help with problems came from abroad. The issue of equipping tanks with radios was raised in different nations in the late 1920s. For example, the French introduced a separate radio operator, turning the Renault NC into the Char D. The first radio-equipped tanks built during the First World War had whip antennas. The French were also pioneers here. However, the Char D1 had a rail antenna. This design was not very antenna-like. It seems to have not worked well, since French tanks returned to whip antennas afterwards. However, rail antennas were used by other nations, including the Germans. After starting a secret tank program in the late 1920s, they quickly arrived at the idea of equipping all tanks with radios. This is why the light tank initially called Kleintraktor evolved from a two-man tank into a four-man one. In addition to a commander/loader, a radio operator was added like on the Char D.

TEKO was mostly used to test the Leichttraktor's radio equipment. Both the radio and the antenna were criticized.

The first German tanks to arrive in the USSR were the Grosstraktor medium tanks built by Daimler-Benz, Rheinmetall, and Krupp. Two prototypes of two different kinds of Leichttraktor arrived in 1930. All of these tanks had radios and rail antennas. The design was quite different than what the French did on the Char D. The German rail antenna was indeed similar to a handrail. They were attached to the fenders, bending around the back of the hull. The antenna was made up of a copper pipe that was held up on composite epoxy rods. This was done since composite epoxy materials are dielectrics. It's no coincidence that composite epoxy materials are used to make circuit boards.

Rheinmetall turret for the Nb.Fz. tank. Unlike Krupp's turret, this one also used a rail antenna.

Experiments that started in 1930 showed a number of drawbacks both in the German radios and their antennas. The issues were gradually resolved and all changes were carefully noted by the Soviet hosts. This saved time and avoided the same issues in the future. For instance, the idea of a spring shock absorber for radios was copied from the Germans. The rail antennas were also analyzed. The German antenna holders were unreliable and the antenna vibrated. The antenna was also often used as a handrail, which resulted in the body bending. The position was also poor, since it easily caught on trees. As a result, the design changed many times.

The rail antenna was used on Pz.Bef.Wg. command tanks until 1942.

One of the key mistakes made by German engineers was the placement of the antenna on the fenders. They were not as rigid as the hull, which caused vibrations. It seems that the testers came to this conclusion, also working on the holders in parallel. The Germans did not discard the idea of rail antennas quickly. The first experimental Nb.Fz. tank had a rail antenna on the turret. The design of the antenna changed a lot. The holders started to look a lot like Soviet ones. This was the result of convergent evolution, since the USSR didn't see a Nb.Fz. until 1939. Either way, by the mid-1930s the Germans focused on whip antennas attached to the side of the hull.

Rail antenna restored at the Vadim Zadorozhniy Technical Museum. This is a good restoration, but the antenna and its holders were not painted.

Rail antennas held on to German tanks for some time. Their last refuge was the Pz.Bef.Wg., a commander's tank on the chassis of the Pz.Kpfw.III tank. Rail antennas were installed on them up until early 1942. They can also be seen on a series of other wheeled and tracked commander's vehicles. They were used in parallel with whip antennas. The holders were improved, but the overall layout was similar to what was used on the Grosstraktor with the wire entering the tank through a port. There was a simple reason for why this kind of antenna disappeared. A tank with "horns" was very easy to see. The Germans were already complaining about this during the Polish Campaign. The whip antenna was much more practical, plus German tankers had the tendency to use the rail as a handrail or a seat. 

The Japanese and the French also used rail antennas to some degree, but the Red Army was their biggest user.

Radio rails, Soviet style

The Soviet field trip for German tanks ended in 1932. Until then, most of the radio experiments were performed on the Leichttraktor. As mentioned above, German experience was widely used in Soviet tank building. Both German and Soviet experience went into designing a new type of tank radio in 1931. The 71-TK tank radio was finished in 1932. An improved 72-TK radio was also built and installed in the PT-1 experimental tank. This was the first Soviet tank with a new generation radio.

PT-1, the first Soviet tank with a rail antenna. A German design was taken as the starting point.

Some people consider the PT-1 an amphibious BT tank. This can only be done out of a misunderstanding of what N.A. Astrov was trying to build. The initial requirements clearly considered the PT-1 to be an analogue to the Grosstraktor, down to the placement of the commander in the hull. The rail antenna was also taken from there. Its drawbacks were already known, and so there were many improvements. For starters, the antenna was attached to the sides of the hull instead of the fenders, which improved rigidity. The holders were also different. The antenna also entered the hull in a different manner.

A similar rail antenna was used on the T-29-4.

The hull antenna as shown on the PT-1 did not go away immediately. It migrated to the tank's successors: the PT-1A and T-29. Trials showed that this was a poor place to put an antenna. The same problems as on German tanks came up, particularly the vulnerability to damage. The T-29-4 lost its hull antenna during trials and the T-29-5 already had a rail antenna on the turret.

The two-turreted T-26 tank had a rail antenna attached to the fenders. Note that Pertinax covers are already installed.

The T-26 tank also had a rail antenna on the hull at the start. The first tanks of this type appeared in 1933. In the case of the two-turret tank, there was simply nowhere else to place it. Only a few two-turreted T-26 tanks with radios were built, but there was enough time for an evolutionary step forward. Pertinax FR-2 covers were added that protected the antenna holders from moisture and dirt. 

Radio-equipped T-37A tanks on parade. Note that the antenna on the rear vehicle is dented. This was a frequent occurrence.

The use of a rail antenna on the hull of amphibious T-37 tanks was also a necessary measure. Like the T-26, it was attached to the fenders, but unlike the T-26 these antennas were very common. 640 T-37/T-37A tanks were built with radios. The antennas were very inconvenient, which is why they are often bent in photographs. They were often used as handrails with predictable consequences.

A typical Soviet rail antenna.

The Soviet rail antenna took its classical shape towards the end of 1933. Factory #174, or rather the OKMO (experimental design bureau) was the main driving force of this process. They were the creators of the "horns" that later showed up on the T-26, BT, T-28, and T-35. All of these designs were about the same since they had the same authors. The antennas went into production in 1934 and never changed significantly.

Composite epoxy rods with Pertinax covers.

The classical Soviet rail antenna was different from the German one. Instead of the hull, it was attached to the turret. Metallic foundations were welded to the perimeter of the turret (6 for the T-26 and BT, 8 for the T-28 and T-35). They were attached at an angle of about 45 degrees, which made the design more robust. Composite epoxy rods were used to hold up the antenna.

A rail antenna restored with the use of original parts at the Museum of National Military History.

The method of attaching the antenna was also different from the German one. The body of the antenna (either a copper rod or a copper tube) was affixed differently. A Pertinax "skirt" was added underneath. Even the Nb.Fz. and Pz.Bef.Wg. did not have such good antenna mounts. A copper pipe was attached to the body of the antenna that then led to an antenna port on the turret roof. This was more reliable than the wire used by the Germans.

The rail antenna on the T-35 tank is the only one in all of Russia preserved in its original state. One can see dents in it, caused in part by the behinds of impolite visitors. Originally, the antenna would not have been painted.

The antenna port was another feature that separated Soviet and German rail antennas considerably. The Germans could potentially install a whip antenna, at least there were experiments to do it on the "tractors". This was a difficult procedure. On Soviet tanks, a whip antenna could be installed from the very start. The installation process was simple and reversible.

A variant with spherical holders used on some T-28 tanks as well as the T-29 pilot tank.

There is one interesting caveat when it comes to both Soviet and German rail antennas. It had to do with the paint. Paint, especially paint from that era, was very conductive. As a result, the antenna and its support rods were not painted, only the welded foundations for the rods. This should be observed by museum restorations and scale modellers. A painted antenna would not work.

A variant used on the T-26.

There is another caveat that has to do with conductivity. Just because the antenna is called a rail antenna, doesn't mean that it can be used as a handrail. In addition to the fact that epoxy and copper are far less sturdy than steel, grabbing the antenna can have an unpleasant side effect. It won't kill you, but the shock will hurt. Don't grab the antenna when the radio is in operation.

A whip antenna could be installed.

There was no major change made to the rail antennas. The biggest change that can be seen was made to the holders for the antenna body. The most common type has two bolts and nuts, but there was also a variant with just one bolt that holds the antenna in place. The T-28 also had a third variant with a spherical holder in addition to the other two. 

Holders for BT-5 and BT-7 tanks.

The BT-5 and BT-7 had distinct antennas. The system was the same as on the T-26 overall, but the attachment of the antenna body to the rods was different. The holders weren't placed above and below the antenna, but screwed into the upper holders with bolts. There is also a second variant that was preserved at the Stalin Line. The bolts screwed directly into the body of the antenna.

Tank at the Stalin Line. The Pertinax covers are missing.

Further development of Soviet tanks resulted in rail antennas falling out of style by 1939. There were several cases, but the visibility of the tank was a major one. A "horned" tank made for a tempting target, plus the rail antennas weren't very practical. Most tanks had their rail antennas cut off, although you still see some in 1941. Only two tanks are known today with original rail antennas. These are the BT-7 tank at the Stalin Line and T-35 tank in Patriot Park. The Museum of National Military History also had restored rail antennas on the T-26 and BA-6. They were restored using original parts and factory documentation.

Tanks with rail antennas could still be seen in the summer-fall of 1941.

In conclusion, let us note that the rail antenna was a symbol of changing requirements. At first, a high-reaching whip antenna was considered a poor idea. However, it was clear that the rail antenna was also far from ideal, and a number of nations returned to whip antennas in the early 1930s. 


  1. So what color should the antenna rail be?

    1. The antenna rail itself can be painted the base colour of the tank.