Osterhagen Project

The Osterhagen Project was a defense weapon consisting of a series of nuclear war-heads placed at strategic points beneath the Earth's crust.

Overview
The Osterhagen Project was a planetary self-destruct system. It was meant to be used only if humanity were suffering unbearably, with no hope or help was ever coming. The Osterhagen system was a chain of twenty-five nuclear warheads placed in strategic points beneath the Earth's crust. If the key to the project was used, the system would be activated and the Earth would be ripped apart.

The Osterhagen keys were distributed among various high-ranking UNIT personnel across the globe. Although the exact number of keys is unknown, there was at least one key for each of the five stations known to be operational. It is also unknown if each key was paired with a specific station, or if a key would operate any Osterhagen station.

General Sanchez was in possession of an Osterhagen key. During the Dalek invasion of Earth, Sanchez authorized Martha Jones to use it if she failed to contact the Doctor. Two other keys were given to UNIT soldiers in Africa and Asia. Given their ages and reluctance to use the keys, it is likely that the two soldiers were junior officers authorized to use the keys by their commanders, just as Martha was.

Osterhagen stations
There were at least five Osterhagen stations located across the world but only three needed to be manned for the system to work.
 * Osterhagen Station 1 located sixty miles outside of Nuremberg.
 * Osterhagen Station ? located in Argentina.
 * Osterhagen Station 4 located in Liberia.
 * Osterhagen Station 5 located in China.

Threatened use
After Earth fell to the Daleks, General Sanchez of UNIT gave a key to Martha Jones, along with the prototype of Project Indigo, to escape. However, former Prime Minister Harriet Jones told Martha Jones not to use the Osterhagen key under any circumstances. (DW: The Stolen Earth)

Believing the Dalek invasion unstoppable, Martha Jones made her way to Germany. She activated the station there and contacted two UNIT soldiers, one Anna Zhou of China, another a Liberian who refused to give his name. UNIT protocol stated that the keys should be used immediately upon the activation of any three stations, but Martha Jones delayed their use to offer the Daleks a chance to surrender. Discovering that the Doctor had been captured, Martha attempted to blackmail the Daleks into releasing him, but the Daleks transmatted her to the Crucible before she could insert the key, disarming the system.

Martha Jones claimed that the Earth would be ripped apart, making the reality bomb useless, since it used Earth as part of its mechanism. After the War in the Medusa Cascade, the Doctor asked Martha to persuade UNIT to dismantle the "Osterhagen Project" altogether, to prevent it being abused in the future. (DW: Journey's End)

Principle
The planet Auros was once found burning by the Doctor and the crew of the Wayfarer. Her captain, Jon Bowman, described the devastation as "The Osterhagen Principle". The planet had been destroyed to stop the Daleks from having it. (NSA: Prisoner of the Daleks)

Other information
It is unknown whether Martha chose not to destroy the Osterhagen Keys out of concern for the welfare of the planet in the Doctor's absence, or if she deactivated the warheads. However, its use on Auros indicates that some trace of information regarding the Osterhagen Project lived on, either through classified files or word of mouth passed down by high-ranking officials.

Little is known of the origin of the "Osterhagen Project". However, the unnamed German woman who provided food for UNIT forces at Osterhagen Station 1 implied that the Project had been around since her visit as a youth to London.

Jack Harkness of Torchwood 3 was able to learn the details of another top-secret UNIT initiative, Project Indigo, but he had no knowledge of the key. (DW: The Stolen Earth)

However, several people outside UNIT knew of the key, such as former Prime Minister, Harriet Jones.

The Doctor surmised the Osterhagen Project and key were invented and named after someone called "Osterhagen". (DW: Journey's End)

Behind the scenes

 * "Osterhagen" is the name of an actual German village, but is also an anagram for "Earth's gone".
 * The concept greatly resembles the Outer Limits episode, "Dead Man's Switch".
 * In the original script, the Osterhagen key was called the "Stattenheim" key. (Doctor Who: The Writer's Tale) Whether this was meant as a reference to the Stattenheim remote control, used by the Second Doctor to call his TARDIS in The Two Doctors, and The Rani to call hers in The Mark of the Rani, is unknown.