The All Terrain Attack Pod, or AT-PT, is a Pentastar Alignment heavy vehicle available throughout the game. It is also available to the Empire of the Hand, New Republic, and Imperial Remnant if they capture an Abandoned Heavy Vehicle Factory. It is armed with a laser cannon.
As the Clone Wars raged on, Galactic Republic army commanders realized the need to build up and diversify their walker armor. One of he new designs was the AT-AP, a highly effective means to transport heavy artillery from place-to-place. Its main function was to serve as a mobile gun platform to shell enemy locations. Although armored, the AT-AP was not designed to function autonomously, and often required support from heavier units such as the AT-TE, Trident, or A6 Juggernaut. Many of these units were used during the final days of the Clone Wars on heavily-defended Outer Rim Separatist strongholds. Some were also used during the defense of Kashyyyk.
During the Galactic Civil War, the Empire slowly phased out the AT-AP in favor of more independent units such as the AT-ST. Abandoned factories formerly used to produce the walkers fell into the hands of Rebels and pirate organizations. AT-APs would continue in Imperial service on the planet of Kashyyyk, where they were used to quell the frequent Wookiee uprisings.
Upon the formation of the Pentastar Alignment, Ardus Kaine saw the need to rebuild an armed force to maintain peace over his new empire. One of the many units called back into service was the AT-PT. Kaine found that by stripping the traditional armament of the walker and replacing it with a single laser cannon it became a cheap and effective anti-vehicle platform. It would serve the Alignment well in the years to follow.
The AT-AP is an anti-light vehicle unit. It fares quite well against armored but unshielded units such as T-1Bs or RAFs. However, anything it can do, a TX-130 Saber-class Fighter Tank or Century Tank can do better. Generally they are a waste of credits, though they can be used in planetary defense quite adequately. Only use these either when absolutely necessary or as a garrison unit.
Obtaining these units for free from an Abandoned Heavy Vehicle Factory (Imperial-style) is a different story, though. These units are free units that are great scouts and harassing units. In addition, they can Hunt For Enemies if there is a problem locating that final bunker full of infantry to win the land battle. In this case, abuse them well.