Hawking Consortium started off their initial mech production by producing this cheap and effective urban defender for the Taurian Concordat, since the traditional Stinger and Wasp mechs , or even their upgraded versions, are poor city fighters.
As their very first entry into the mech market, Milton Hawkings knew he had to have a credible product, and one that was desperately needed.
As the Fighting Urukhai rampaged through Taurus a few months back, he saw his chance. Playing on the TDF's sudden awareness of their lack of city fighting capability, he offered them a cheap mech to solve their problems.

Designd from the very start as a light and cheap city fighter in the mold of the oft-maligned Urbanmech, the Concrete Rat is nevertheless far more effective, armed with a variety of weapons and capable of handling almost any city combat situation.
A single extended range large laser provides it with some ranged firepower in case it ever found itself outside a city.
More important for its role, though, are the array of lasers, machine guns, short range missiles, and flamers. They enable the Concrete Rat to effectively eliminate infantry, vehicles, and other units quickly and efficiently.
The speed of the mech was kept low in order to save up enough space for the weapons. Jump jets were mandatory for any urban fighter, and the Concrete Rat mounts three of them.

The Concrete Rat received its baptism of fire during the initial stages of the Taurian Civil War, as units loyal to Grover Shraplen poured into Taurus to hunt down Ian Calderon.
The Taurian Guard, equipped with many Concrete Rats, and under the personal command of Calderon, engaged Shraplen's forces in a series of brutal ambushes.
Even though outnumbered more than two to one, Calderon's careful use of his Concrete Rats allowed him to destroy a significant portion of enemy infantry and vehicle strength, as the Rats were armed with infernos for their missile launchers.
In the end, the Guard held out long enough for reinforcements to arrive.

Captain Fiona Regault
Commander of a small militia unit in Samantha when the Civil War erupted, Captain Regault sided with Ian Calderon and fought throughout the battle for Samantha from her Concrete Rat 'Templeton'. She took down more than a company's worth of vehicles and infantry in the bitter street fighting that occured..
While Fiona is sad at having to kill so many of her fellow Taurians, she is adamant that she carry out her duty no matter what her personal feelings.

Concrete Rats are found in many Taurian Concordat units, and some Magistracy units as well. 1st Corps contains the most, about a battalion's worth.
Hawkings Consortium has an exclusive contract with the TDF for the Concrete Rat, and it is unlikely that non-Trinity Alliance units will have access to the design.