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Mobile Pill-Box Fortress

United States of America (1940)
Mobile Pillbox – None Built

The early 20th century was dominated by new technologies being developed in large numbers. To capitalize on these rapid advancements, monthly magazines were published that focused on bringing these new technologies to the general public’s attention. This proved to be a great success. The most popular example of these magazines is Popular Mechanics, which published its first issue in 1902 and continues to be published today. Another popular example was Modern Mechanix, which went through several name changes since its first issue in 1928 before its final issue in 2001.

The technologies featured in these magazines varied greatly in their application. Power sources, home gadgets, farming equipment and flying machines are but a few examples of the kinds of inventions and concepts featured. Most notably, particularly during both World Wars, was the inclusion of conceptual weaponry and armored vehicles. These were rarely competently designed. Due to a total lack of practical insight into the use of military equipment, the end result was often a design more appropriate for a science fiction setting than a real battlefield. Some designs featured in these magazines are notable for their relative practicality however, at least when compared to the rest, and their intended usage is somewhat reasonable for being designed by illustrators as nothing more than magazine filler.

Firepower Required

Before the United States entered the War in 1941, it faced a distinct lack of dedicated tank destroyers. While it would not be until late 1941 when the US finally adopted such a vehicle – the 75 mm gun-armed M3 Gun Motor Carriage – designs already existed in the previously mentioned magazines that were intended to fill a similar role.

The November 1940 issue of Modern Mechanix features a drawing of a large armored truck with two guns in an even larger turret-mounted behind the cab. This Mobile Pill-Box Fortress, as it is referred to in the magazine, by virtue of having a single turret on a sensible and presumably existing truck chassis, is on the higher end of practicality regarding conceptual designs found in these magazines. No other name is given to the vehicle and no further information on it can be found despite supposedly being based on a prototype built by a truck manufacturer based in Los Angeles, California.

The single page showing the Mobile Pill-Box Fortress and its description. Note the inconsistency in scale between the crewmen in the cab and in the turret, making judging the size of the vehicle difficult. Source: Modern Mechanix, Issue November 1940.


The Mobile Pill-Box Fortress is based on a large truck chassis with two single wheels at the front and two pairs of triple wheels at the rear. The reason for two pairs of triple rear wheels should be clear, as directly above them is a huge domed turret housing a pair of 6 inch (152 mm) guns, presumably naval in origin.


The turret can rotate a full 360 degrees, but gun elevation and depression are not known. Depression would inevitably be limited in the forward arc due to the roof of the cab and the bizarrely located headlight mounted to it. Ammunition for the guns is stored in two racks, one upper and one lower. The shells are stored nose-up in two racks that run the full circumference of the interior turret wall. This allows a large number of projectiles to be stowed despite their great size. It is not shown in the drawing where the propellant charges are stored. It is possible they are stored at the front of the turret or on the right side of the guns where they would be obscured, but the most likely explanation is either that they were never considered by the artist or the shells are one-piece. No access hatch or door is visible on the turret.

Due to the great recoil generated by such large guns, the vehicle features four large outriggers around the turret ring. These outriggers appear to be telescopic in extension and fixed in place with no articulation, apart from being capable of extending and retracting their feet up and down. The outriggers are an appropriate design choice for a vehicle that, as the name suggests, acts as a stationary pillbox instead of a more mobile vehicle, capable of quickly relocating during combat.

The turret’s gunner is located on the left side of the guns and has no seat. He has a direct vision telescope that is mounted unusually far back in the turret which is aiming through a thin visor in the turret’s mantlet. Even though the sight would most likely move with the mantlet, and stay lined up to see through it, the field of vision as a result of being mounted so far back would be incredibly narrow. Only two other crewmen are shown in the turret, those being the loaders, who are each loading their respective guns. As 6 inch guns, each projectile would have been very substantial, at likely 45 kg (99 lb) or more in weight. With the turret having a pair of guns, this means that each loader has to lift and load projectiles by himself, which during sustained fire would be incredibly tiring without any loading aides such as a winch or conveyor, neither of which are shown.


The cab is located at the front of the vehicle. The driver’s position is assumed to be on the right side due to the placement of the only seat visible in the drawing, an unusual choice for an American vehicle. However, due to the perspective of the drawing, the seat may actually be more centered in the cab. On the left side of the cab is the assistant driver who operates at least one of the two machine guns present in the vehicle, both of which are in the front corners of the cab. Ammunition for the machine guns is stowed above the engine in the center of the cab. Due to the placement of the driver, it is likely that he operates the right-side machine gun instead of the assistant driver having to move back and forth between the two guns. Like some tanks with an assistant driver, it is likely that he would be expected to take over driving the vehicle should the driver be injured. They may also alternate duties each day.

There are a number of vision ports around the cab. There are two ports on the front slope which can be hinged open. Similarly, there is a large hinged port on the sloped roof. It can be assumed there is a second port on the right side which is obscured, but what these upwards-facing ports would be for is not clear. Each of the two machine guns in the front corners had their own fixed vision ports above them, which, like that on the turret, would provide undoubtedly poor visibility for those operating the guns. There is a fixed port on the left side of the cab, again it is likely the right side has the same. Lastly, there is a vision port in what appears to be an access door in the back left corner of the cab. A step is present below it on the outside, as is a handle. What appears to be two hinges spanning the width of the cab roof are also present. It is not clear how these panels would open.


No specific armor values for the vehicle are given, but while the drawing is poorly scaled it is clear that the armor of the turret is supposed to be very thick by standards of the time. The turret armor is intended to protect against shells and bombs (no specific shell or bomb is described), whereas no such requirement is given for the cab armor, but it is reasonable to assume it would be at least capable of resisting small arms and shrapnel. The engine has its own armored housing within the cab, and it is not known if the covers over the wheels are simply mudguards or if they too are supposed to be armored.

Fate And Conclusion

While at its core the Mobile Pill-Box Fortress is reasonably designed by the standards of the magazine it was featured in, no information can be found regarding the claim that it was based on a real prototype that underwent four months of testing by the US Army. After the United States joined the war, a great deal of effort went into developing and testing trucks carrying anti-tank guns in a wide variety of configurations.

The purpose of these vehicles was to be fast and easy to manufacture due to being built on existing chassis, as well as fast on the battlefield, able to quickly respond to reports of enemy tanks in an area and move to engage them. This manufacturing and doctrinal need are incredibly similar to the description of the Mobile Pill-Box Fortress, a truck-based vehicle capable of traveling up to 65 mph (105 km/h) to any threatened area to counter both tanks and infantry, and afterward, relocate to any other area in need of anti-tank support. However, due to the great weight of the vehicle, it is reasonable to expect it to be incapable of reaching such high speeds outside of long straight roads.

The choice of a 6 inch gun would be questionable, let alone a pair of them. The incredible capability of such weapons against both tanks and infantry cannot be understated, especially for 1940, but their immense size and weight directly influences the size of the vehicle, which in turn condemns it as almost entirely impractical. For the vehicle’s time, it can be argued quite easily that no practical advantage comes with having such large weapons in a vehicle like this, simply because far smaller and lighter anti-tank guns already existed that were perfectly capable of defeating any tank of the period. At the very least it would be easy to invent a more sensible gun for the drawing.

Despite the similarities between the purpose of the Mobile Pill-Box Fortress and the actual tank destroyers the United States would come to use, the sheer unwieldiness and weight of the vehicle would undoubtedly restrict it to roads only, greatly limiting its application as a strategically mobile weapon. The design, like so many from these magazines, is a great example of theory detached from reality and it is no surprise that none were ever built – this vehicle was purely for the readers of the magazine rather than actual use.

Representation of the ‘Mobile Pill-Box Fortress’ produced by the Author, Mr. C. Ryan, funded by our Patreon campaign.


Crew At least 5 (Driver, Assistant Driver, Gunner, Two Loaders)
Speed 65 mph (105 km/h)
Armament Two 6 inch (152 mm) guns, Two machine guns


Modern Mechanix, November 1940

15 replies on “Mobile Pill-Box Fortress”

I don’t wish to be rude but you guys put this up and don’t have an entry for something like the BMP series?
It seems a very odd choice.

i don’t wish to be rude but info about BMP can be found very easily online. This on the other hand is an oddity that you don’t read about every day.

Hello James, a bit more of an in-depth answer here.
First off, we have full editorial freedom in picking our topics. We extend the same freedom to our writers, as they can decide what they write on for themselves. We do not tell them what to write. While we do encourage them to tackle well-known subjects and even offer bounties on certain articles (when we have the cash), we do not force them to do certain topics.

As for the BMP series, we used to have articles on all three of the major ones (BMP-1, 2 and 3), however, all three of them have been withdrawn recently (along with 400 other articles) because they were no longer meeting our standards of historical accuracy. The illustrations are still available on the respective nation or era pages.

We will be rewriting these, but it will take time, as properly researching, writing and editing new articles takes a lot of effort. Also, we are encountering significant difficulties in finding good sources on Soviet vehicles (we are currently banging our heads with one of the BTR series).

If you would like to help, you can add the vehicles you would like to see on our website to our Public Suggestion List and you can help by adding more sources (or other suggested articles)
Also, in order to help us with illustrating and publishing, please do consider donating through Patreon or Paypal.

If you feel brave enough, we always need more writers!

They used to have those. However back then tanks-encyclopedia was little better than reading a wikipedia article. I’m glad that they had raised their standards. With time, most well known articles will come back, just have patience.

could you guys do an article on the “hen and chick” tank concept? i found that there wasn’t much information other than pictures

Obviously a made up design by an artist. Shells are twice the weight of modern day shells. Massively heavy structure is built on a truck. Guns alone could weight 15 tons. Whole armament can easily go as much as 20 tons. Minus armor, superstructure and weight of vehicle itself. I find it hard to imagine any common truck back then being able to move this monster at all. Even nowadays such trucks as shown here have no more than 8 tons of carrying capacity. In order to have anything better you need a highly specialized trucks, but those weren’t available since late cold war.

In general, while an idea of making your bunkers mobile is an attractive one. It falls apart quickly when you realize that digging a hole, making a cement wall and putting a gun there will always be a lot cheaper than constructing an expensive engine, complicated suspension system and maintaining said vehicle. Fortifications are what they are, because they can afford to add as much weight as they wish. This makes them inherently vastly superior to all mobile elements. For example, these 6 inch guns were quite easily and cheaply placed in ground fortification. Such fortification would outrange any self propelled artillery by simply being bigger. They would be well armored. They would be a lot cheaper. In order for an mobile element to be as good you need to create extremely complicated machinery. See super heavy projects like Dora guns, T95, superheavy guns and superheavy tanks who were born out of need to break through those fortifications. Extremely heavy, extremely impractical, but that is the only way how you can outmuscle a bunker. That was the reason why Maginot line was so vastly successful. It would cause so much headache for attackers that they would rather break neutrality of other nations, fight whole new coalition of enemies rather than try to break through fortified position.

I want to elaborate on the idea behind mobile bunkers. It is just my random ideas and they are unrelated to topic at hand. I enjoy exploring reasons behind why this vehicle was conceived. It is the idea of using mobile fortifications in war. Field of thought which the military had put into surprisingly little consideration.

I never saw this concept properly explored as mobile bunkers when they were employed had enjoyed great combat success. Remember T-34 in dug in positions? I think that if done properly, a mobile bunker can be a real asset to an army (at least to WW2 to cold war era), if expensive one.

Here is my idea. Produce mobile bunker like a Maus. However, instead of making it full blown superheavy tank, instead create it with an idea of field assembly and disassembly. Theater armies would establish specialized heavy tank maintenance facilities near the frontline (supplied with specialized equipment and machinery). During preparations for major offensives, these facilities would receive parts of such tanks. They will come in assembled modules. One part is suspension/engine. Another is superstructure, etc. These facilities would assemble these individual parts into a functional superheavy and would disassemble it when it is damage or battle is over. In this way you would have a superheavy tank who is cheaper to maintain, a lot easier to repair and can act as a mobile bunker. Its engine would allow it to change positions on a battlefield during downtime. Its lack of mobility would be unimportant, however it could in return possess far thicker armor and more weaponary than a normal tank. This is just some whacky idea which is more trouble than it is worth, but I do enjoy thinking of what if.

Another idea which I had is to actually transport parts of a bunker into the frontline. Guns, walls, foundation, all of those things come in part. When during preparation period engineers could do field work like digging the ground, preparing cement and putting in pre-fabricated fortifications into their place, quickly assembling a bunker. Preferably, bunker would be designed in such a way that later it could be easily demolishing and salvaging those parts for further use. Initially I had this idea for modern day use. Soldiers are living in shipping containers or occupy civilian infrastructure. Both are more dangerous to soldier’s life than having nothing at all if base comes under fire. I had this idea of soldiers transporting small deployable, individual cover in order to fortify strong points and individual foxholes/firing positions. In addition, I wanted to replace use of sandbags in making pillboxes and other fortifications for soldiers on a field by giving them prefabricated walls to place those sandbags around or to reinforce existing civilian infrastructure with military grade protection wherever they go.

The Germans in world war II had about excactly what you described.

Two of the examples used at the front line are the Machine gun nest and the well known Panther Turret.

The armoured machine gun nest was as its name implies a small heavily armoured cupola like structure, mounting one MG. it was carried around on specially built horse drawn carriage so it could be tipped over onto its emplacement (mostly a reinforced hole in the ground)

The well known Panther turret had a version with a bolted steel base. So you had to dig a hole, bolt the base in it together and lift the turret in place on it.

I think with something in the weight range of a Panther turret is the maximum practical stationary turret that you could move around somewhat easily and put in place without resorting to ultra heavy mobile cranes.

Ofc, these were always static weapons, so you’d better hope that the ennemy attack is coming in that spot. Also once discovered they were easily taken out by a “normal” artillery. So they were ambush weapons at best, only holding up the advance for a short while.

Therefore one can ask , why have all the cost/materials/emplecement logistics etc involved when youcould basically do the same thing with a standard towed AT gun. (which hopefully could even bugger out before the return fire started coming in)

Also this sort of construction is most useful to nations on the defensive. It is these nations that need every tank they can build. Since building a tank turret is a substantial portion of building one can again as: would it not be better to go the whole way and build the complete tank anyway. (for the turrets you also need to have a lot of transport and engineering vehicles)

This was the fate of the static Panther turret: Its construction did bite into Panter tank construction and due to the limited usefulness of the static turret and the hassle involved in installing it, the army opposed having them at all and preferred (fewer) complete tanks over some of these turrets.

I think looking at the practicality of the design, one should take a look at what a typical twin or even single 6″ gun mount weighs. About the only data of that period we have here is from naval mounts. Ill put the single mounts in here too, since these are usually hand worked and thus closer in concept what this “mobile fortress would be.

You have to take into consideration that mounts listed here have at best light splinter protection (typically in the 5 mm – 8 mm range) with with open backs for the singles, . The duals I list here are eiter closed turrets with splinter protection or open backed shielded mounts.
I’m also including some mounts in the 5″ calibre range.

German mounts: Single 15 cm mount (Tbts KC/36) : 16 ton
Twin Drh LC/38 : 61 tons
British: Twin 4,7″ destroyer mount: 25,8 tons

US: Single hand worked 6” mount : 19 tons
Twin with elctrical taining and elevation : 52 tons
Twin 5″/38 cal low angle mount, with 6 mm splinter protection: 29

Note that none of these include heavy armour or ammunition storage, a single 15 cm is in the 40 kg range. So just 100 shells for two guns (which i consider is the absolute minimum and would only allow one serious engagement at best would add in another 4 tons…

So you are certainly right in considering this design completely unpractical.

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