The inner German border was a complex system of interlocking fortifications and security zones long and several kilometres deep, running from the Baltic Sea to Czechoslovakia. The outer fences and walls were the most familiar and visible aspect of the system for Western visitors to the border zone, but they were merely the final obstacle for a would-be escapee from East Germany. The complexity of the border system increased steadily until it reached its full extent in the early 1980s. The following description and the accompanying diagram describe the border as it was around 1980.
Travelling notionally from east to west,Because of the changes in direction of the border, it could also be crossed north to south, south to north or even west to east in some places. an escapee would first reach the edge of the restricted zone (Sperrzone), a closely controlled strip of land 5 kilometres (3.1 mi) wide, running parallel with the border. Evading the patrols and watchful inhabitants of the Sperrzone, the escapee would have reached the first of the border fences. The signal fence (Signalzaun), around from the actual border, was lined with low-voltage electrified barbed wire which activated alarms when touched or cut.
Beyond the signal fence was the "protective strip" (Schutzstreifen). It was brightly lit by floodlights in many places to reduce an escapee's chances of using the cover of darkness. Guard towers, bunkers and dog runs were positioned at frequent intervals to keep a round-the-clock watch over the strip. Crossing the Schutzstreifen, the escapee would next reach the floodlit control strip, often called the "death strip" in the West. Tripwire-activated flare launchers were situated at various points to help the border guards pinpoint the location of an escape attempt. The last and most formidable obstacle was the outer fencing. In some places there were multiple parallel rows of fences, each up to several metres high, with minefields in between. The fences were not electrified but were booby-trapped with directional anti-personnel mines at intervals of , each one of which was capable of killing at a range of up to . Finally, the escapee had to cross whatever natural obstacles were on the western side of the border fence as well as traversing a strip of cleared ground that was up to 500 meters (1640 ft) wide. While crossing this outer strip, the escapee would appear in clear view and shooting range of the border guards before reaching the safety of West German territory.
Restricted zone
The Sperrzone, a wide area to which access was heavily restricted, was the rear segment of the border defences. When it was established in May 1952, it included a number of villages and valuable agricultural land. Although the land continued to be farmed where possible, many of the inhabitants were expelled on the grounds of political unreliability or simply because they lived inconveniently close to the border line. In some instances, entire villages were razed and the inhabitants relocated far to the east.Rottman, pp. 20–21
Those who remained behind were required to be completely loyal to the regime and support the border guards, helping them by watching for strangers and unfamiliar vehicles. Even so, they had little freedom of movement; special permits were required to enter the zone and farmers worked under close supervision. They could enter and leave the zone an unlimited number of times but could not travel to other villages within the zone.Buchholz, p. 57 Curfews were imposed to prevent inhabitants from crossing the border under the cover of darkness.
The Sperrzone was not fenced off but was marked with warning signs. The entry roads were controlled by checkpoints (Kontrollpassierpunkte) through which only authorised individuals could pass. The first layer of border fences, the signal fence, lay on the far side of the Sperrzone to control access to the protective strip or Schutzstreifen adjoining the border itself.
Signal fence
The signal or "Hinterland" fence (Signalzaun) was the first of the border fences, dividing the Sperrzone from the more heavily guarded protective strip (Schutzstreifen) adjoining the actual border. Its purpose was to provide the guards with an early warning of an escape attempt. The fence itself was not a particularly formidable obstacle, standing only high. At the top, middle and bottom, rows of electrified barbed wire strands were attached to insulators. Cutting the wires or pulling them out of place resulted in an alarm being activated, alerting the guards to a possible breach of the fence. In practice, though, the border guards found that the fence frequently malfunctioned. The signal fence also had a control strip on its eastern side. The fence was built on open high ground wherever possible, to ensure that intruders would be silhouetted against the sky and thus be more easily spotted. By mid-1989, of signal fencing had been constructed along the border.Rottman, p. 29
Watchtowers and bunkers
The border defences were monitored from hundreds of watchtowers regularly spaced along the Schutzstreifen. Initially they were simple wooden huts mounted on legs between high, usually constructed from locally sourced timber. Most were replaced with concrete watchtowers from the late 1960s onwards in conjunction with the upgrading of the border defences.
By 1989, there were 529 concrete towers along the length of the inner German border and a further 155 towers of steel and wood construction, as well as various little-used observation platforms in trees. The concrete towers were prefabricated from sections that could be assembled within a few days. Their height could be varied by reducing the number of sections as required. They were connected to an electricity supply and telephone line and were equipped with a powerful 1,000-watt searchlight (Suchscheinwerfer) on the roof that could be directed at targets in any position around the watchtower. The windows could be opened to enable the guards to open fire without leaving the tower. In addition, the towers had firing ports emplaced in the side walls below the guard compartment.Rottman, p. 28
The towers were principally of three types:
The BT-11 (Beobachtungsturm-11, "Observation Tower-11") was introduced in 1969. Standing high on a concrete platform, it was constructed of eleven interlocking circular segments with walls thick. The guards were stationed in an octagonal observation compartment at the top, which was accessed via a steel ladder running up the inside of the column. Each face had a firing port below the windows. The tower's top-heavy construction made it unstable and there were incidents of BT-11s collapsing in high winds or after heavy rain had softened the ground under the foundations.Rottman, pp. 27-28 On the Baltic coast, where 27 BT-11s were constructed to overlook the East German seaboard, the towers had to be evacuated in force 6 () winds."", Grenzturm Kühlungsborn The BT-9 (Beobachtungsturm-9, "Observation Tower-9") was introduced from the mid-1970s to remedy the defects of the BT-11. It was constructed in a similar fashion but its square profile and lower height, at , made it more stable. The four-sided guard compartment at the top had distinctive copper-tinted windows. Each face of the tower had a firing port on the stage below the guard compartment. The Führungsstelle or Kommandoturm ("command tower") was a shorter and rarer type of tower that served as the command centre of a border sector. It contained monitoring and control equipment to open border gates remotely, turn on and off fence lighting and alert lights, rotate searchlights and so on. Disturbances of the signal wire and detonations of SM-70 booby-trap mines would be detected by the command tower. The towers were topped with long-range radio antennae to communicate via R-105 radio to other units. A distinctive feature of this type of tower was the prominent air intake box at ground level.
Around a thousand observation bunkers also stood along the length of the border.Ritter, p. 69. Most common was a small concrete bunker known as an "earth bunker" (Erdbunker), usually recessed into a depression in the ground with a view along the guard road and border fence. It was constructed from two base sections, each high with a cross-section of . It terminated in a third section that had two firing ports in the front side and one or two on each of the other sides. The roof was a separate component nesting on top of the concrete bunker, which could accommodate up to two soldiers.
Guard dogs
Dog runs (Kettenlaufanlagen) were installed along high-risk sectors of the border. The dogs were generally chained to steel cables up to long. The dogs were occasionally turned loose in temporary pens adjoining gates or damaged sections of the fence. By the 1970s, there were 315 dog runs with 460 dogs. This figure increased steadily until a total length of of dog runs had been installed by mid-1989,Rottman, p. 29 with 2,500 dogs employed as watchdogs and another 2,700 so-called "horse dogs".
Patrol roads
Rapid access to all parts of the border line was required to ensure a quick response to escape attempts. This was initially a problem for the East Germans, as few patrol roads existed along the border in its early years. Patrols typically used a footpath that ran inside of the fence, alongside the control strip.
When the "modern frontier" was constructed in the late 1960s, an all-weather patrol road (Kolonnenweg, literally "convoy path") was laid down to enable the guards to travel rapidly to any point along the border fence. It consisted of two parallel lines of perforated concrete blocks, each block measuring approximately wide and long. The blocks were pierced with four rows of rectangular concrete drainage holes. In some places they were laid crosswise to provide a continuous roadway. They were also occasionally used as foundation stones for structures such as towers and revetments and to create foundations on which towers were constructed.Rottman, p. 23
The Kolonnenweg usually ran between the control strip (on the border side) and the watchtowers (on the inland side). Around of patrol roads were built along the border, of which around was fully paved. In addition to the main Kolonnenweg, there were numerous short access roads built through forests and fields in the Schutzstreifen. Constructed from the same perforated concrete as the Kolonnenweg, these gave the border guards rapid access from the hinterland to the border line. Some civilians were permitted to use these access roads for forestry or farm work, though only with special permission.Display materials, Grenzdenkmal Hötensleben
Control strips
The control strips (Kontrollstreifen) were lines of bare earth running parallel to the border fences. They were not an obstacle as such but provided a simple and effective way for the border guards to monitor unauthorised travel across the border. It was almost impossible to cross the strip without leaving footprints, enabling the border guards to identify otherwise undetected escape attempts. They could learn how many individuals had crossed, where escape attempts were being made, and at which times of day escapees were active. From this information, the border guards were able to determine where and when patrols needed to be increased, where improved surveillance from watchtowers and bunkers was required, and which areas needed additional fortifications.