100 Ton Mouse
After the fall of France in 1940, German designers got access to French developments, including full scale models of superheavy tanks, the FCM F1 and ARL Tracteur C. Compared to these tanks, the German VK 65.01 (Pz.Kpfw. VII) that started development in January of 1939 seemed obsolete. It's possible that this discovery led to the cancellation of the mild steel prototype.
Under the same index, a new, more powerful tank was designed. It seems that this is the tank mentioned in the intelligence report sent to the Red Army General Staff, dated March 11th, 1941. This report triggered work on the KV-3, KV-4, KV-5, A-44, and made serious ripples in other directions. The 90 ton mass fits in with later information about the vehicle known as VK 70.01. It really had a 105 mm gun and the mass was limited to 90 tons (the current limit of German railroad platforms).
Another confirmation that the VK 70.01 started its life before the fall of 1941 is the correspondence with Krupp regarding a new, even more powerful, 149 mm gun, which started no later than April. This same gun, with a length of 40 calibers, pops up again in November of 1941. The "heavy tank type VII" turned out to not be disinformation, fed to Soviet intelligence.
The vehicle that Soviet intelligence discovered wasn't anything like the commonly known VK 70.01. The hull and turret with sloped armour appeared only in late 1941, after the Germans ran into Soviet T-34s. Despite the index suggesting the vehicle was in the 70 ton class, the mass of the vehicle varied from 70 to 90 tons.
The same thing happened to the armament. The "canonical" version of the VK 70.01 is dated late January of 1942, and by early March, the project splintered. The VK 72.01 appeared, with either a 105 mm L/70 gun or 150 mm L/35 gun.
In September of 1939, the tank commission (Panzerkomission) was created, which acted independently of the 6th Waffenamt. It was headed by Ferdinand Porsche. A conglomerate headed by Porsche K.G. was in charge of conceptual design. The conglomerate also included Steyr-Daimler-Puch, Friedrich Krupp AG, Siemens-Schuckert AG, Skoda, and Nibelungenwerk, which were responsible for the engine, hull, electronics, suspension, and assembly, respectively. On March 22nd, 1942, this conglomerate was tasked with development of another 100 ton tank. This project was indexed VK 100.01.
According to preliminary classification, the 100 ton class tank would have a 15 cm KwK L/40 gun with a capacity for at least 100 rounds. A part of the ammunition would be stored in the rear of the turret. Initially, the rounds would have been two piece, but a sketch of a one piece round was attached to a letter regarding the turret, dated April 18th, 1942. The overall length of the round was 1.6 meters, and it weighed 57.4 kg, 34 of which were for the shell. This was the lightened variant: initially, the 15 cm K18 round was used, which weighed 43 kg. The muzzle velocity of this shell was 875 m/s, and the rate of fire was an optimistic 4-5 RPM. As an alternative, the 12.8 cm KwK L/50 was proposed, with a 29.3 kg shell and 810 m/s of muzzle velocity. The design of the VK 100.01 was to be done by May 15th.