With the Capellan Confederation's recent developments in Arrow IV FASCAM technology, supply of the powerful artillery missiles has outstripped demand in recent months.
The deployment of Catapult and Raven teams, while extremely effective, also places a great strain on the Capellan treasury, as each pair comes in at more than 10 million C-Bills.
Unwilling to spend so much on these mechs, Chancellor Liao has ordered Ceres Metals to come up with alternative models that can cheaply deliver Arrow IV missiles onto the battlefield. He also wanted Home Guard units to have a chance at using the new technology, as Ravens and upgraded Catapults are rarely seen outside of regular and line units.
Ceres Metals eventually developed the Chang Gong(longbow) and the Shan Zi(dice), with a combined price tag of slightly more than 5 million C-Bills.

The Chang Gong has only one objective: to launch Arrow IV missiles. To this end, it has two tons of Arrow IV ammo, which is used for two different ammunition types by savvy commanders. Favourite combinations are Inferno-IV and Vibrabomb-IV ammo mixes, as well as FASCAM and Homing. Because of its small ammo capacity, the designers copied the O-Bakemono in having an ammo canister reloading system, for quick reloading in the midst of battle.
Capable of 85 kph at top speed, the Chang Gong can elude killer teams with its Apple Guardian ECM system, essential equipment considering the propensity of headhunter teams in recent years.
Ceres Metals gave it a standard engine for improved durability, but used endo steel structure to save weight for more equipment. The addition of an ER medium laser was solely for the pilot's peace of mind, not for any real combat effectiveness.
Considering the amount of ammo it carries, CASE was another indispensible feature. There had already been two incidents where the CASE saved the pilot and the mech from total destruction.

A raid by Capellan March forces in 3067 on Capella found the Davion troops surprised by the sudden emergence of Shan-Zi and Chang Gong artillery teams, a last ditch attempt by Liao commanders to protect the factories. Faced with a deluge of Arrow IV missiles raining from the sky, the Davion mechs quickly tried to retreat, only to find their way back to their dropships blocked by FASCAM rounds delivered by the Arrow missiles.

Chang Gongs have been deployed throughout Home Guard units in Liao space, with priority going to units on the Marik border. Several frontline units have been spotted using the mech as well, loath to use their expensive Catapults in some risky situations.
Several Chang Gongs along with Shan Zi spotters have been sold to the Magistrcy of Canopus, as well as the Taurian Concordat. Apparently, Protector Grover Shraplen was so impressed that he tried to persuade Sun-Tzu to build a Chang Gong/Shan Zi factory on New Vandenburg.