Tradecraft: The cache

Washington, DC (TFC) – The art of hiding supplies for later use was perfected by two groups. Most modern militaries rely on the techniques used by these two organizations when training their own soldiers for “stay behind” operations. One of the two groups perfected the techniques for hiding their supplies in rural settings, the other developed effective means for hiding their equipment in urban environments. Those two organizations are the Viet Cong and the Irish Republican Army.

Why would you need to hide something?

Pick a reason; there are millions. It could be something as simple as wanting to have precious metals stored somewhere other than the house to protect them in the event of a break in or robbery. It could be the desire to safely store your firearms out of reach of children. It could be to have a last line of defense in the event of invasion. Most people, however, want this information to prepare for the inevitable zombie apocalypse.

Cache vs. Slick

These two methods are related, but are very different. They both involve placing your supplies in a secure location that is hidden. The difference is the length of time the supplies are intended to be stored and the ease at which they can be retrieved.

Cache: Tubes of buried weapons hidden from an occupying force, supplies of food hidden along an evacuation route, valuables hidden from potential burglars, etc. These supplies are intended to be hidden away for years or decades, and time can be taken to retrieve them.

Slick: A firearm hidden inside a fireplace, a “burner” prepaid cell phone hidden behind a light switch plate, a large quantity of currency hidden beneath a floor board, etc. The supplies are hidden in locations where they can be retrieved within seconds or minutes rather than hours. They can also be easily returned to their hiding locations.

The Cache

The easiest way to approach learning these techniques is to learn how to cache the two most difficult items to keep operational during long-term storage. The most difficult items are electronics and firearms. If you learn to successfully cache these types of materials, you will be able to cache anything. The reason these items are so difficult to store secretly for long period of time is because they have to be kept extremely dry, clean, and within a comfortable temperature range.

Selecting a location: The number one mistake people make when selecting a cache site is giving in to the desire to have it on their own property. The desire stems from worrying about it being discovered by accident. If you’re worried about somebody discovering it accidentally, it will certainly be discovered if somebody is looking for it.

One of the worries when selecting a location is construction occurring at your cache site a few years after you store your supplies. The easiest way to mitigate this is to choose a location where construction is forbidden without changes to zoning ordinances or environmental protection laws. Wetlands, national forests, state parks, graveyards, along railroad tracks, the habitats of endangered animals, sites protected for their historical significance, etc would provide you with notice long before construction ever begins. The other option is choosing a location that has already been developed and won’t likely be expanded anytime soon. As odd as it sounds, the grounds of government buildings are perfect locations. The IRA cached weapons on the grounds of post offices, schools, waste treatment facilities, monuments, libraries, and so on. These locations are rarely expanded upon and when they are, there is always a public debate over the use of the tax dollars for the expansion, which again provides you with the opportunity to move your supplies before they are discovered. Religious buildings are also wonderful locations, because of the stigma attached to searching a church, mosque, or temple.

Weapons cache recovered by IDF. These weapons were not properly packaged. Image source: IDF

Weapons cache recovered by IDF. These weapons were not properly packaged.
Image source: IDF

Preparation of contents: The principals discussed below are specific to firearms and electronics. If these same techniques are employed with any other form of supplies, they will work. In most cases, you will be overprotecting your material. Firearms and electronics must be kept clean and dry. All of the material needs to be cleaned thoroughly prior to being sealed. In the case of firearms, it is important to wear powdered latex gloves during the cleaning, drying, and packing phases. This isn’t to conceal your fingerprints; it is to keep the oils from your hands from sealing moisture against the metal of the firearm. Moisture is your number one enemy because it creates rust. Once the item is properly cleaned and dried of debris, it should be lightly oiled. While electronics don’t need to be oiled, all other procedures hold true. Even a small amount of moisture can damage sensitive electronics over time. The addition of moisture absorbing material like silica gel packets can provide an added layer of protection.

Sealing the contents: Each item that is to be cached should be sealed individually. This prevents one item that has moisture trapped in it from damaging other items in the cache. The best method of sealing the contents individually is to seal the cleaned and dried item using one of the many commercially available vacuum sealers. If you have removed air and moisture, you have prevented rust. The US Army Field Manual on caches uses techniques borrowed from the Viet Cong. It was written before vacuum sealers were widely available. It suggests wrapping your materials in aluminum foil, then wax paper, then sealing the wrapped package with rubber, tape, or wax. Wrapping your already vacuum sealed package in this method will provide an outstanding level of protection.

Choosing a container: There are hundreds of options to choose from when thinking about a container in which to place your sealed contents. The most widely-used container is a PVC pipe that is capped and sealed at both ends, but any container that meets the following criteria is acceptable:

Watertight and airtight
Resists shock
Strong enough to support the crushing weight of dirt
Able to withstand rodents or insects
Capable of withstanding acidic or alkaline soil

It is best to test to see if your container is watertight prior to concealing it by placing it in a bathtub filled with hot water and watching for emerging air bubbles. Cold water can cause certain materials and sealants to contract. Cold water may not reveal all weaknesses.

Burying your cache: When it finally comes time to bury your cache is the moment when you are most exposed. People can’t see you do it, or they can steal it. If in wartime, opposition forces may capture you (and your supplies) while you are paying attention to digging. There are methods of lessening these risks. One is to perform the digging under cover of night with sentries watching for passersby. When a passerby approaches, the digging crew is informed by the sentries, and all activity ceases. The diggers hide until the intruders are gone. At night, movement attracts our eyes. If there is no movement, the likelihood of being seen and remembered is greatly lessened. The other tactic, which was used to great effect by the IRA, is to conduct the hiding phase in broad daylight and in plain view.  A group dressed as workers would enter a library or school, head to the boiler room, and install pipes that were filled with weapons during the workday. The pipes appeared to be part of the structure, so they were left alone. Since the pipes were not functional, they never needed repair and were left undisturbed. This same technique could be employed by disguising yourself as groundskeepers or road crews.

The top of your container should be an absolute minimum of 18 inches below the surface. Below 18 inches, the ground temperature stays relatively constant throughout the seasons. Extremes of hot and cold are one of the most detrimental things for ammunition. If kept at a constant temperature ammo can stay good for decades. Now is not the time to get lazy.

Not burying your cache: As mentioned above, not all caches are buried. Some of the best hiding places are in plain view. They typically require a lot more planning and material, but examples that have been used successfully by people in the past include disguising PVC pipes packed with material as part of a filtration system for a large artificial pond, placing containers inside hollow pieces of concrete yard art before sealing the hole on the bottom, and the IRA even erected a fake utility pole using the metal buckets that once held transformers to hold weapons and explosives.

When to bury: If time permits, the best time to bury your cache is in the spring just prior to a rain. The rain helps wash away tell-tale signs of the disturbance. As vegetation springs back to in the spring, it helps mask the dig site.

Disguising burial site: The best method of camouflage is blending into the surrounding landscape in such a way that looking for caches in the area is either absurd, like in a library, or in a location that is simply too inaccessible to believe people would hide something there, like in swampy wetlands. If that option isn’t available, the best you can do is to leave the scene as close as possible to what it looked like when you arrived. Photos prior to disturbing the scene can aid in recreating the appearance.

Marking the site: Many people mistakenly believe they will always be on scene to lead others to the cache personally and don’t take the time to develop an accurate way of telling someone else where the cache is. If you are wounded, someone else may have to retrieve your cache. Obviously the simplest method is to obtain GPS coordinates for your cache. However, if a GPS system is unavailable at the time of recovery, you are left depending on somebody’s ability to properly use a map to get within one foot of the coordinates. Remember that most people can’t find Wal-Mart without their navigation system today. The overwhelming majority of people have no idea what the terms “minutes” and “seconds” have to do with locating a place on a map or how to convert what their GPS shows them into what is seen on a map. Why would they? It’s a dead language. If you’re interested in learning the Sanskrit of navigation, the conversion formulas can be found here. The best method is to talk like a pirate. An example of directions to actual cache site:

“Ten paces from the front door, fifteen paces to the left, roughly halfway between you and the lion.”

This information can be openly spread on the internet without fear of someone finding it, because they haven’t been given the starting location. Unless, of course, people happen to know the name of one of the high schools I attended and were interested in discovering a time capsule that is to be opened in 2096. Caches don’t necessarily have to contain something survival or war related.

People searching for your cache: In the event that someone is looking for your cache, for whatever reason, and they have a general idea of where it is buried, they will use one of two tools. They could use either ground penetrating radar or a metal detector. As with most pieces of technology, the key to defeating it lies in knowing its capabilities, and using those capabilities to defeat the human operating it. The easiest way to defeat a metal detector search is to bury random pieces of scrap metal throughout the area about 18 inches below the surface. The operator will eventually grow tired of digging a hole to find an old alternator or metal pipe. They may give up the search simply out of irritation. You can further protect yourself by burying your caches 36 inches below the surface and placing a piece of scrap metal over it about half way between the surface and the cache. This will lead the operator to believe he has found what he is looking for and move to the next location.

US soldier searching for weapons caches in Iraq. Image Source: SSgt. Edward A. Reagan

US soldier searching for weapons caches in Iraq.
Image Source: SSgt. Edward A. Reagan

Ground Penetrating Radar (GPR) is a much more advanced system that basically measures the electrical conductivity of the ground. Large pieces of metal are more conductive and therefore show up on the radar screen. GPRs can effectively search 15 meters down. So unless you rent heavy excavation equipment you can forget about burying it deeper than it can “see.” Scattering random scrap metal around the area will give the operators a lot to investigate, however the GPR provides a visual representation of the scene and the operator can judge by size whether or not to investigate. Your best bet is to either place your cache somewhere they won’t use GPR, like wetlands or actually in a pond (remember your cache is waterproof), or place it in a location that leads them to believe the anomaly they see on their screen is something other than what it is. If your cache is directly below a water pump for example and the pipe is buried vertically, the anomaly will likely be ignored as part of the pump system. Another technique for disturbing GPR is to increase the conductivity of the ground. GPR is severely limited “by less-than-ideal conditions. The high electrical conductivity of fine-grained sediments (clays and silts) causes conductive losses of signal strength; rocky or heterogeneous sediments scatter the GPR signal. Another disadvantage is that data collection is relatively slow.”

The same thing happens with an area that has drastically varied conductivity. If you can’t select a site with high or varying conductivity, you can alter the ground’s conductivity yourself by scattering Epsom salt over the area in different amounts. The salt increases the conductivity of the surface and helps to diffuse the signal. The signal travels through the first few inches of soil very quickly and then slows down this provides the operator with false signals. In theory, mixing salt with the dirt while you are covering your cache site will increase conductivity and make the operator of the GPR believe the “anomaly” is just inches below the surface, when it is actually several feet below. It should be noted that this is completely theoretical as far as I can tell, and there is no evidence of this ever actually working. Of course, that may be proof that it does work because nobody has ever reported finding or losing a cache disguised in this manner.

Conclusion: If you need to keep something hidden for extended periods of time, you now know the basic procedures. Whether it’s something as simple as a duplicate set of personal documents, an arsenal to fight off armies of the undead, or food and medical supplies to use in the event of natural disaster, you now know the basics. Like most things, you are only limited by your imagination.