Two Letters Re: How to Defend a Retreat Against Wheeled Vehicle Threats

CPT Rawles:
From a former Army Combat Engineer’s perspective, I would disagree with some of the information about anti-tank ditches and agree with other points raised in the article; How to Defend a Retreat Against Wheeled Vehicle Threats, by B.W. in Pennsylvania.
In the U.S. Army we would build a ditch at least 1 meter deep and typically closer to 2-3 meters deep with D7 bulldozers.  The ditch would be right around a blade width wide.  The most effective method is a dozer team with one digging it out and the other coming perpendicular to push the spoil to the side.  A key note is that the spoil, excavated dirt, was placed on the friendly side not the enemy side.  This concept is counter to original letters description of exposing the underside by placing the spoil on the enemy side of the ditch.  I would reason that most in a survival situation would not fight armored forces anyway and would further not have the firepower to penetrate even the bottom of a main battle tank (MBT) or even an armored personnel carrier (APC).  One reason for placing the spoil on the friendly side is that it increases the height of the obstacle.  Tanks are impressive and powerful but their ability to scale a fairly straight wall is limited.  The other key doctrinal reason for placing the spoil on the friendly side might not be overly practical from a survivalist viewpoint but it is to aid the friendly forces in breaching their own obstacle in the counter-attack.  As you counter-attack your engineers can roll up and push the spoil back into the ditch to create a crossing point.  Defense is only a temporary measure until you can go back on the offensive.
I would very much agree that tangle foot is highly effective for people on foot.  Wire obstacles are easy to stockpile material for (Class IV) and fairly easy to install.  To make any obstacle effective it is best covered by direct fires (rifle fire).  Most would not be able to cover obstacles with indirect fire (mortars, artillery, grenade launchers). If possible place your close in obstacles (tactical obstacles) outside of hand grenade throwing distance, typically 30 meters, from your positions.  We won’t probably face many factory hand grenades but improvised ones and especially Molotov cocktails are a real danger to most structures. 
The combat engineer field data manual (FM 5-34) is a extremely valuable reference tool for all types of engineering tasks.  It gives good basics on tying in obstacles to terrain.  How to build obstacles with various intents to include disrupting, fixing, turning and blocking the enemy from certain avenues of approach.  The information and data is just about endless. – J.B. in Arkansas


Mr. Rawles:
B.W’s How to Defend a Retreat Against Wheeled Vehicle Threats was a great bit of information and as my retreat is not far off a two lane highway, it is something I think about often.

There are several good US Military archives on booby traps from the Vietnam Era.  Many of these can be found free on the internet.  They provide hundreds of ways to detect and avoid and disarm vehicular and anti-personnel traps.  These are the same IEDs (as well as new and improved) that are being used on our troops in Afghanistan.  To prevent legal questions there are no plans provided herein but many of these are of simple construction and common sense.

One common method that was not discussed was speed bumps.  These are very easy to construct and still allows common traffic.  It may not stop a vehicle but it will disorientate unprepared drivers allowing you more time to respond.

Police also use multiple ways to stop vehicles.  Spike strips can be purchased on line for around $400.  These are portable devices that can be deployed to slow down any vehicle with standard inflatable tires.   There are also plans on the internet to make homemade spike strips.  However, an easy spike strip can be created with nails driven through a plank of wood with a second blank backing it to prevent the nails from retreating when encountering hard rubber.  In situations where you have roads blocked with other vehicles, this can create an easily removable obstacle that allows you to utilize the road but can catch a speeding intruder unaware.  Many of us have also experience spike strips at rental car and parking lots that allows vehicles to travel one way without danger.  These retractable spikes can also be built or purchased.  Spike strips can be created in a variety of way.  However vehicles can still drive on rims and this only slow the vehicle down and reduce control. 

The military is also using a version of the spike strip called the X-Net by QinetiQ which is made of a high tensile material that wraps around the axle of the vehicle after puncturing the tire.  They are also using SQUIDs (Safe Quick Undercarriage Immobilization Devices) which are high tension straps that entangles the vehicle’s axles.  There are videos on YouTube on how both of these work.  While there are no plans and I couldn’t even find them for sale, it is good to be aware of them.  The SQUID may be able to be developed but at this time I have not researched it thoroughly.

B.W.’s tanglefoot plan with stakes and wire is a great antipersonnel device.  However, this same thought process can be applied with heavy chain or steel cable within a wooded area using the trees as support.  A 1,000 lb. chain wrapped around trees will significantly damage and disable most vehicles.   These can also loosened and remain on the ground as little or no obstacle and then be tightened at need with the help of a motorized vehicle or even a pull-along and then braced securely into the tree.

There are also motion detectors, sonic and light alarms.  Whiles these do not disable a vehicle it allows you to have more response time and may distract or disorientated an unprepared driver.

Lastly, several years ago in Wisconsin a snowmobiler was decapitated by fishing line or wire strung at head length across a trail.  While this is irresponsible and a sure way to get in a huge lawsuit in today’s world, in a defensive Crunch situation, it is a cost effective way to minimize intruders.

These few items combined with what B.W. has already discussed provide more options for slowing intruders.  The goal is to control the ability of individuals to approach you with the various combinations allowing you to turn the tide and attack from ideally defensive areas.
I just finished Survivors and it was very enjoyable.  Thanks for everything. Best Regards, – Don V.

JWR Adds: As I describe in my latest novel “Survivors”, the now obsolete Magic Cube flash camera cubes are striker fired, so they can be added to tanglefoot obstructions. You simply tape them on to a post or stout rod with clear packing tape, and attach a paper clip to the the striker arm in the Magic Cube’s base. The paper clip is in turn attached to a trip wire. Voila, you have a device that will both alert defenders and frighten and disorient nocturnal intruders. Sometimes simple technologies can be very effective. This is also a non-lethal and non-maiming technique, so it is one that can be used in situations where the rule of law still exists.

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