Let's start with Entertainment Bible 2, the first place (outside of B-CLUB magazine) where the Proto Zeta Gundam appeared. Here's an excerpt from the book's "MS Development History" section:
Entertainment Bible 2 also has a brief profile for the Proto Zeta itself in the "MS Design Collection" section at the back of the book:Entertainment Bible 2 wrote:Knowing of the existence of the Gaza, Anaheim and the AEUG decided to introduce this transformable mobile suit concept into the so-called "Zeta Project," a program to develop a high-performance mobile suit which would serve as a symbol of both organization. Design changes were made to the movable frame of the MSN-00100 Hyaku Shiki, which had entered development after the Rick Dias, in an attempt to add transformation mechanisms. However, the attempt failed and it was changed back to a normal mobile suit. This was because they had tried to achieve a fairly complex transformation, for which they needed to accumulate more data.
Thus the MSA-005 Methuss and its simplified transformation mechanisms were created. A prototype machine was completed with little difficulty, making it possible to obtain data, but its mobile suit form was of a very different style from previous machines. After the completion of the MSZ-006X Proto Zeta Gundam, the Zeta Gundam officially entered development. However, although there were no flaws in the transformation mechanisms, excessive metal fatigue was observed while operating in mobile suit form. It was determined that this was a defect in the design of the frame itself.
As the program was struggling, Anaheim took delivery of the Gundam Mark II developed by the Titans. Although this wasn't even a second-generation machine, the novel design concepts of its movable frame, and the design plans stored on the floppy disk that accompanied it, triggered a hasty reevaluation of new machine types. This led to the completion of the MSZ-006 Zeta Gundam, a transformable mobile suit which could change into a wave rider with atmospheric entry capabilities.
Entertainment Bible 2 wrote:MSZ-006-X1~X3 PROTO ZETA GUNDAM
The prototype of the MSZ-006. Transformation mechanisms have not been introduced at this point.
So far so good. The profiles from the Entertainment Bibles were then compiled into the MS Encyclopedia, which features a longer profile for the Proto Zeta:
The early editions of the MS Encyclopedia also included a mobile suit development flowchart which indicated that the Hyaku Shiki was based on the Proto Zeta. Remember that for later.MS Encyclopedia wrote:The prototype of the MSZ-006. It had already been rolled out by the time Anaheim received the RX-178. This machine was developed as a non-transforming model. The MSZ-006 was completed in a short time using the frame and avionics from this machine.
More recently, the Proto Zeta received a longer profile in the G Generation game series:
G Generation F wrote:An AEUG prototype attack mobile suit. This is one of the prototype machines created as part of the Zeta Project, Anaheim's new mobile suit development program. The predecessor to the Zeta Gundam, it was originally developed as a non-transforming mobile suit. However, the company's development of transformable mobile suits accelerated when it obtained the movable frame technology of the Gundam Mark II, and this machine was redesigned as a transformable model. Using the frame and avionics from this machine, the Zeta Gundam was completed as a transformable mobile suit. Although the X1's head is a Hyaku Shiki type, there is also an X2 model with a Dias head and an X3 model with a Nemo series head.
The Master Grade Zeta Gundam kit manual pretty much repeats what we already know:
MG kit manual wrote:March, U.C. 0087. Having captured the RX-178 Gundam Mark II from a Titans facility, the AEUG obtain movable frame technology from this machine, and meanwhile develop the Flying Armor as an atmospheric entry option. Then, after the Jaburo landing operation, a Zeta Gundam with the ability to transform into a wave rider is completed, using the previously developed MSZ-006X type as a base.
And then finally, we have the recent Data Collection 5, whose "MS Development History" says the following:
Data Collection 5 wrote:The Prototype Zeta Gundam that served as a development base for the Zeta Gundam was a machine developed before the capture of the Gundam Mark II, and it incorporated Anaheim's distinctive block buildup concept. This was meant to improve production and maintenance efficiency by dividing each part of the machine into a separate block. However, making each part independent created many problems, and improvements to the control system were also evaluated in other machines. The base design of the Hyaku Shiki was created by adding the movable frame concept to this machine. Then, by incorporating the plans provided by Kamille, it was redesigned as a transformable mobile suit.
Ultimately, it proved possible to complete the Zeta Gundam in a very short time by using movable frame construction for the modules required for transformation, while taking the necessary weapons, generators, and so forth from the prototype version. Meanwhile, the Flying Armor was developed to evaluate the atmospheric entry capabilities which were the Zeta Gundam's most distinctive feature, and this was introduced into combat during the capture of Jaburo.
In other words, all these sources agree that the MSZ-006 Zeta Gundam was created by adding Gundam Mark II movable frame technology and wave rider capabilities to the non-transforming Proto Zeta Gundam. But past that, things get pretty confusing.
Entertainment Bible 2 says that the Proto Zeta was developed after the Hyaku Shiki and the Methuss, perhaps just to gather data on the Zeta Gundam's mobile suit form (which couldn't be obtained with the Methuss). But Data Collection 5, and the development flowchart in the early MS Encylopedias, claim that the Hyaku Shiki was actually based on the Proto Zeta, and that the Zeta Gundam wasn't originally supposed to transform at all. The G Generation profile likewise says that the Proto Zeta was originally developed as a non-transforming machine and was only redesigned as a transformable type after the developers obtained the Gundam Mark II's movable frame technology.
So where does this leave the Hyaku Shiki? Well, although we have a couple of claims that it's based on the Proto Zeta, most other sources seem to agree that it's just a "rival candidate" for the Zeta Gundam which failed to pass muster as a transformable mobile suit. While it's often described as being a spinoff of the Zeta Project, it doesn't seem to have had a direct influence on the design of the Zeta Gundam itself.
-- Mark