Bulgaria's police arrested two German nationals and a Bulgarian army major over stealing a vintage tank produced by Maybach, owned by the Ministry of Defence.
In November the group dug up the old German tank from the time of the Second World War, put in the ground near the southern Bulgarian border in order to be used as a stationary gun, authorities reported.
In December the suspects tried to steal another buried up Maybach from the same region near the town of Yambol but the police prevented the crime.
Experts said there are few tanks of the same type in the world still outside the military museums and the thieves could make a good profit by selling the machines to collectioners.
One of the tanks has already been exported from Bulgaria.
Police is still investigating how the Maybach crossed the border.