The Thunderlizard class photon artillery was a type of mobile siege unit used by the military of the Romulan Star Empire.
They were noted as being one of the most feared vehicles on the battlefield and were a showcase of sophisticated as was common with Romulan designs. A unique photon shelled delivery system allowed the artillery to fire its deadly payload from the centre of the craft rather then be mounted on a turret. This provided stability for the artillery and allows the firing of more powerful shells into enemy lines.
The front of the craft housed the anti-gravity drive as well as the necessary sensory equipment. This allows this artlliery to strike enemy positions and then quickly escape any possible retailiation. This raiding tactic works well with the Romulan use of cloaked tanks during combat engagements.