18 BBY/2IY: Supreme commander of the Imperial Fleet, Lord Vader ordered the execution of Queen Apailana of Naboo on the charges of committing treason against the empire by harboring fugitive . The 501st was sent to eliminate her but the battle became a disaster the empire for a number of unexpected setbacks: On the land the 501st was shocked to see that the defenders of Naboo was leaded by their former brethren's from the from the famed Torrent company, the most veteran company of the 501st under the command of the traitors captain CT-7567 "Rex", the former second-in-command under Lord Vader. Under his command the Naboo defenders put up a deadly resistance and then lunched an even more deadly counterattack that drove them from the planet. In the bloody engagement, the 501st lost an entire battalion, entirely composed of veteran troops from the clone wars and Operation: Knightfall.
While the ATL-10 was well suited for defending fortification and repelling attacks, it was ill suited for supporting any form of attack. With that in mind the, Vader instructed the design team to create a solution using the resource they had and he “insisted” that the unit was to be ready as soon as possible. Fortunately for that small group, they had already had a concept ready to be put to test. They took a Hammer chassis, and got rid of the entire turret section. A portion of the front armor was cut open and the gun was installed onto the hull. The tank retained the targeting system and electronic suite of the Hammer but an extra crewman was added to work as the loader. The prototype was ready days before Vaders “Inspection” so the team was spared from any “misfortune” but rather handsomely rewarded for their efforts. The system perform admirably in battlefield, largely replacing the ATL-10 in offensive operations, while the ALT-10 became the fulcrum in Empire’s effort to defend it planets form enemy attacks.
On that note, this unit will probably go though a MAJOR redesign.
I'll probably relocate gun on a fixed casemate as part of the main hull.