The project began in 1934, and bore fruit in 1938 when the first successful prototype was tested. Allied intelligence got wind of the project shortly thereafter, and nicknamed the tank the "trencher." Allied scientists attempted to create their own tanks with tunneling capability, but the only "trencher" used by the Allies during the war was a unit captured during a mission behind enemy lines.

A couple dozen Tunnelpanzers were produced, but many were lost attempting to navigate mine fields. In late 1939 the Allies had developed a deep-mine that could be buried deep underground, safe for humans and surface vehicles but deadly for the Tunnelpanzers. The most effective use of the Tunnelpanzer was infiltrating spies and saboteurs behind enemy lines, and returning with important prisoners. Rommel also made use of the Tunnelpanzers in Afrika, where he was able to create several deadly ambushes for Allied armor with them.

Most of the Tunnelpanzers that survived the war were dismantled for spare parts. Some fell into the hands of geologists, and spelunkers, who made use of them as research vehicles once the guns were removed, and the life support systems were replaced with more efficient systems that would allow them to remain underground for a week or more mapping massive cave systems, and the intricacies of the Earth's crust. These modified Tunnelpanzers were sometimes called "crust crawlers" or even "trenchers," by scientists who borrowed the term from the Allies.

TUNNELPANZER (Tunnel Tank)

Each of the Tunnelpanzers has a similar configuration. They make use of a standard panzer body style, with a wedge-shaped prow. It has two treads mounted on each side, one on top of the other, which rotate in opposite directions. This provides propulsion from both the top and bottom of the tank when it's underground. A giant screw mounted on the front of the tank breaks up the ground in front of it, pushes it out from the body of the tank, and provides some propulsion. The main gun is secured against the main body of the tank when it goes underground, and can be deployed one round after surfacing. The machine gun retracts completely into the hull.

Viewports that allow the crew to see out and aim the guns are closed and sealed when the tank is underground. While travelling beneath the surface, the crew can navigate by using an inovative 'seismic radar' that sends and receives vibrations through the ground to probe for obstructions, determine the distance to the surface, and basic geographical features above them. Life support will provide 24 hours worth of air for 4 crew members, before it is necessary to surface.

The crew of the Tunnelpanzers consists of a crew commander, a driver, and a gunner, with a position provided for one auxiliary crew member or passenger. Tank crews were given careful psychological exams before being allowed to train or serve aboard a Tunnelpanzer. Many were eliminated for the intense claustrophobia that can develop after several hours beneath the Earth's surface.

Tunnelpanzer I: The initial Tunnelpanzer was a functional piece of armor, that met all of the tank commander's criteria for a tunneling model. It was the more numerous of the two models, being produced in small numbers through 1942.

Tunnelpanzer II: The second Tunnelpanzer model was created to allow the crews a longer range without refueling as well as a larger gun. Tank commanders would not accept a slower model, despite the weight gain necessitated by the improvements, so it took until 1941 to develop an acceptable version. This model was produced in small numbers through the end of the war.