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Dead drop spike
Dead letter box

Perhaps the most well-known device for a dead drop, or dead letter box, is the so-called dead drop spike, a watertight metal container, usually made of aluminium, with a sharp tip at one end and a removable cap with a piece of rope at the other end, giving access to a small storage space. In the German language a dead drop spike is known as Erddorn and in Dutch as a trapcontainer.

The dead drop spike can best be described as a hollow nail. It comes in many flavours: short, long, thick and thin. The one shown here is a narrow one that is suitable for passing money, One-Time Pads (OTPs) or small documents, for example between an agent and his handler.

The spike can easily be hidden by the owner, simply by pushing it into the ground in a known place, e.g. between some plants, or in the grass, with the short pieces of rope (or leather as in this case) sticking out at the top. It will hardly be noticable between the existing grass or plants.
  
Dead drop spike - opened

The sharp tip at the bottom allows the spike to be pushed into the ground easily. If the ground was too hard, the agent could even step on it in order to 'drill' it into the ground completely. The removable cap at the top gives access to the actual container in which the message was hidden.

The removable threaded cap has an O-ring that makes it watertight. Small objects, like the OTP booklets shown here, could be stored inside it.

Once the spike was placed in the secret location, the sender had to notify the recipient that a message was waiting for him. This was usually done by leaving a secret mark (signal) at at a predetermined place, for example a white cross written with chalk at the side of a phone booth.

The recipient then went to the secret location and collected the spike by pulling its strings.
  
Removing the OTP booklets from the 'spike'

After that, he confirmed reception by leaving another secret mark at a predetermined place. This way, sender and recipient (or agent and handler) never had to meet in person and were less likely to get caught by the counter-espionage agency of the country in which they were operating.

During the Cold War, spikes like this were often used for passing One-Time Pads, or OTPs, that were needed for encoding and decoding secret messages. Other types of dead drop spikes were much thicker and some even had space for one or two 35 mm photo films. The dead drop spike shown above is a high-quality reproduction made by Dereu & Sons Manufacturing Co. (US) [1]. This company also produces high-quality hollow coins that can be used to hide a memory device.

Dead drop spike Unscrewing the head Dead drop spike - opened Dead drop spike - open Watertight head removed Removing the OTP booklets from the 'spike' Dead drop spike with OTP booklets Dear drop spike with OTP booklets
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Dead drop spike
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Unscrewing the head
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Dead drop spike - opened
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Dead drop spike - open
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Watertight head removed
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Removing the OTP booklets from the 'spike'
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Dead drop spike with OTP booklets
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Dear drop spike with OTP booklets

Names
Dead drop spikes are known under different names in different languages. Here are a couple of popular ones that we've come across:

  • Dead drop spike
    English
  • Erddorn
    German
  • Briefstift
    German
  • Trapcontainer
    Dutch
References
  1. The Dereu & Sons Manufacturing Company, Dead Drop Spike
    Retrieved August 2015.
Further information
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Crypto Museum. Created: Tuesday 04 August 2015. Last changed: Tuesday, 13 June 2017 - 10:51 CET.
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