A Wardrill (also known as Combat Drill in other countries) is a type of armored fighting vehicle built for the purpose of trench digging and underground warfare. They are planning something

History:

Wardrills were invented in the early 1920s after the introduction of the tank and were originally used for construction work as Tunnel Boring Machines.
When the Quelvic War broke out, these machines were converted in order to make trench digging easier.
The first attack wardrills were developed following the introduction of the Anti-Wardrill mine and the advent of modern tunnel warfare.
To address environmental concerns, new classes of wardrills are capable of filling in the tunnels that they make.

Model of the first Luminerran produced Type-A wardrill (dubbed Steven, thanks Crilland) on display in the Luminerran Museum of Technology (not-to-scale)

Types

Wardrills are generally separated into four types.

Wardrill docks are called "Molehills", when a Wardrill parks, it first has to surface in a designated spot before moving towards its parking space.

In Luminerra the first Wardrill Battlegroups were named after animals such as Moles, Groundhogs, Ants, etc. There are 8 battlegroups in total which are themselves composed of 4 Wardrills.

Anti-Wardrill Mines

Anti-Wardrill mines were made in the 1930s in order to combat the increasing use of wardrills. They are usually placed in a wardrill-made tunnel with the use of a Type-C "Interceptor" in the hopes that the wardrill that made the tunnel would pass by.

Environmental Concerns:

The use of Tunnel Boring Machines as weapons of war has come under scrutiny over problems like increased cave-ins from unfilled tunnels. As a result the new Wombat Class of Luminerran Wardrills are made to be able to fill in the tunnels they leave behind when needed.