It has the same power, speed, and price as the Claymore Sword, but it is swung in different arcs.
In order to unlock the weapon, you
either need to own the full version of Dwarfs!? or unlock the "Not a War hammer" achievement in the free version.
The axe can be seen embedded in the ground on the Moon Base map. However, this is just set decoration, and the axe cannot be picked up regardless of if you've unlocked it or not.
Currently, the only way to unlock the axe legitimately is to own the full version of Dwarfs!?.
Previously, there was an alternate method with the free version of Dwarfs!? (aka Dwarfs!? FTP). The free version has it's own separate achievements from the full version. Obtaining the "Not a War hammer" achievement in the free version used to be an alternative way to unlock the axe. However, a recent change to how Steam handles privacy settings made it so that Killing Floor can no longer read the Dwarfs!? achievements and so this no longer works.
As a result, the "Gimli That Axe!" achievement is impossible to achieve, as it only unlocked by detecting the "Not a War hammer" achievement in Dwarfs!? FTP.