The seven-ton Mouse ultra-light tank was merely a transitional model — a stopgap to fill the armored force's vacancy. Production was low. Built by the Northern Heavy Industries Group, a total of only 198 units (including test prototypes) were manufactured before the production line shut down.

As the very first generation of mass-produced tanks, the Mouse ultra-light tank had many problems:

1. **Insufficient firepower** — armed with only a single 7.92mm machine gun. Later improved variants switched to a 12.7mm machine gun or 20mm autocannon, but firepower remained weak. Armor was also too thin, capable only of stopping standard machine gun rounds.

2. **Only three crew members**, placing excessive burden on each.

3. **Early models' gasoline engines lacked horsepower**, making the tank too slow. Improved variants equipped with new diesel engines showed improvement.

From the outset, however, the Mouse tank was intended as an initial attempt at tank mass production, a technology demonstrator, and a proving ground for the nascent armored force's tactical doctrines. It was quickly replaced by the Fox light tank.

As a technology demonstrator, the Mouse ultra-light tank had low production numbers but many variants — designated alphabetically from A through J. The A model was the initial service version, armed with a single 7.92mm machine gun, using the famous Christie suspension, with 198 units produced from the T4 prototype.

The B, C, and D models involved only mechanical and structural adjustments. The E model was a major revision: an entirely new transmission, along with a newly developed 110-horsepower air-cooled diesel engine. The E model received a 12.7mm machine gun; the F model got a new turret and a 20mm autocannon.

Each improvement was carried out by retrofitting tanks already in service, with low numbers for each variant. The final definitive major overhaul was the G model, which by this point bore so little resemblance to the A model that the original design was virtually unrecognizable.

In 1930, all 180 Mouse ultra-light tanks equipped by the 1st Training Division were recalled to the factory for comprehensive overhaul to the G standard. As a result of this event, surviving A through F models are extremely rare — only the few preserved at Northern Heavy Industries as reference vehicles and a small number of ten F models exported to Korea.

After 1932, all G-model tanks were withdrawn from the training divisions and reassigned as training vehicles for the armored schools.

After the revolution in Japan, 150 of these G-model tanks were provided as military aid to Japan. After factory overhaul, they were sold at a symbolic price of one yuan, and out of a "somewhat embarrassed" sentiment, the batch received an entirely new designation: H.

The I model was an experimental vehicle fitted with a Fox tank turret mounting a 37mm gun — only one prototype existed.

The J model was likewise experimental, with frontal hull armor thickened to 45mm. However, numerous problems emerged during testing and the project was canceled. Only one prototype existed.

These two sole surviving prototypes — the Mouse I and J models — now stand in the China Tank Museum in Tianjin, alongside fifteen different T-series prototype verification vehicles, their gun barrels raised high, silently telling visitors the story of Chinese tank development.

The Cat ultra-light tank used a Vertical Volute Spring Suspension system (the same type as the M4 Sherman tank) and was produced and deployed simultaneously with the Mouse.

The Cat ultra-light tank was the Mouse's competitor, entering service at the same time — a product of the special circumstances of China's exploratory tank design period. Although both were products of the Northern Heavy Industries Corporation, the Cat's tank factory was located in Guangzhou, Guangdong, while the Mouse's "mother factory" was in Tianjin. They were products of two design departments under one parent company.

At the time, the Chinese military was locked in fierce debate over which suspension system to use. Each had its strengths and weaknesses. In the end, Chen Ke made the call: develop both simultaneously and let real-world field testing settle the question.

The Mouse's three shortcomings were equally present in the Cat. However, due to the different suspension, the Cat ultra-light tank offered slightly better crew comfort — though this was purely relative; early tank interiors were universally miserable. Thanks to this advantage, the Cat was more popular with armored troops than the Mouse. Compared to the Mouse's sub-200 production run, the Cat reached 400 units. Of these, 180 were exported to Germany under the designation "agricultural tractors," becoming the initial armed nucleus of the newly formed German armored forces.

The Cat's improvement program ran in parallel with the Mouse's. Weapons and powerplant upgrades were synchronized. Because the Cat's turret was designed from the start to be "as large as possible," it avoided the Mouse's problem of needing turret redesigns — interestingly, the turrets used on the Mouse F and G models were actually Cat turrets. Hence the Mouse G earned the nickname "Cat-Headed Mouse."

Like the Mouse, the Cat had variants from A through H. The A through F improvements mirrored the Mouse's. The export-to-Germany version was designated the G model, though the Germans used their own domestically produced gasoline engines. From the macro perspective of tank development, switching from diesel to gasoline engines was a regression — but given Germany's heavy dependence on synthetic gasoline, it was a necessity. After the switch to lower-vibration gasoline engines, the German Cat G variant actually had the best crew working environment of the entire series.

The H model showed no major changes from China's domestic F model, merely replacing the 110-horsepower air-cooled diesel engine (shared with the Mouse) with a water-cooled diesel. Approximately 30 F-model Cats underwent this modification, of which twenty were exported to Thailand.

Both the Mouse and Cat were seven-ton ultra-light tanks. As transitional products of the startup phase, neither was perfect — but China's first generation of armored troops was born in these two "cradles."

The types that truly formed the backbone through mass deployment were the Fox light tank and the Wolf medium tank. Together, they constituted the main force of China's 1930s tank corps. By the standards of the other timeline's later classifications, even fifteen-ton tanks would technically be classified as "light." But in the mid-1930s, among all the world's tanks — setting aside each nation's handful of multi-turret monstrosities — the fifteen-ton Wolf was practically the heaviest there was.

As a transmigrator, Chen Ke's vision for Chinese tank development was not one of overambitious leaps. He honestly required his researchers to progress step by step — "a few tons at a time" — steadily increasing weight, with gun calibers rising in lockstep. As a materialist, Chen Ke believed that technological progress was inseparable from long-term accumulation. The joke of India's Arjun tank from the other timeline was something he would absolutely never allow to happen in China.

After comparative field trials of the Cat and Mouse, the "Armored Forces Committee" ultimately chose the Cat's suspension system for the next-generation tank.