This is a gundam papercraft from a chinese design studio papertang. The scale of this paper model is 1:100. The HT-01B Magella Attack tank was the main battle tank of the Principality of Zeon's ground forces throughout the One Year War.
Magella Attack used a powerful 175 mm cannon for their main purposes of combatting the Earth Federation's M61 Main Battle Tanks and later mobile suit forces. A 3-barrelled 35 mm machine gun, for attacks against infantry, rounded out the armaments. The Magella Attack's most distinguishing feature is a very large canopy-style cockpit very similar to fighter aircraft, which is very unusual for a tank but gives the men inside a more open view of the battlefield - in fact this cockpit, called the Magella Top, is designed to be detachable along with the entire main gun system so that the pilot could continue fighting in case the tank's hull was destroyed. In reality, the Magella Top was little more than a poorly qualified escape vessel with a gun, lacking the fuel to stay afloat for more than a few mere minutes.
Even when compared to the M61, the detachable top design of the Magella Attack severely limits its main gun's range of traverse to the point that Magella Attacks almost exclusively relied on maneuvering its hull for targeting, more like a casemate assault gun than a true main battle tank. Then the advent of RGM-79 GM rendered Magella Attack tanks, as other weapons that preceded mobile suits were, mostly ineffective. But when properly deployed, however, the Magella actually scored victories against mobile suits by the virtue of its 175 mm main gun being capable of destroying enemy mobile suits with a well-placed shot, and even lunar titanium alloy armors can be penetrated or seriously compromised from a direct hit.
Finally, Zeon engineers, motivated by the increasing shortage of all weapons during the late stage of the One Year War, were able to come up with some interesting contraptions. Magella Attack main guns were known to be jerry-rigged into hand-held weapons for MS-05 Zaku Is and MS-06 Zaku IIs as a stand-in for the standard 280 mm Zaku Bazookas, and the hull assembly can be fused with the torso of a Zaku into the Zaku Tank, which came as a blessing to many Zeon forces that found themselves left with little more than spare parts or salvaged components. Abandoned Magella hulls, as part of a Zaku Tank or otherwise, proved to be a particularly versatile platform capable of being outfitted with items ranging from weapons such as missile launchers to engineering equipments such as dozer blades.
You can download this gundam paper model from here: Gundam Papercraft - HT-01B Magella Attack Free Download