Between the Tiger (VK45.01) and Tiger II (VK45.03), Henschel developed an interim concept for a Tiger with frontal armor sloped back at 50 to 60 degrees from the vertical. (Frontal armor sloped at less then 40 degrees was also suggested.) At a meeting at Kassel, Germany, on April 15th and 16th of 1942, Henschel, Krupp, and Wa Pruef 6 decided that, because there was no machine gun ball mount that could be attached to such slopes at the time, the VK45.02 would have a slit in the armor a machine gun could be fired through. (The same solution was used on the Panther Ausf.D.) The VK45.02(H) would be armed with Porsche's VK45.02 turret, the same turret used on the first 50 serial Tiger IIs, and an 8,8cm KwK 43 L/71 cannon.
As production plans for the Tiger II were being finalized, Henschel was still under contract to produce 424 more Tigers. It was deemed intolerable that so many Tigers needed to be produced before Tiger II production could start. Henschel's solution to this was that they would make 330 more Tigers, then switch over production to the VK45.02(H), producing 170 units. After these 500 tanks, Tiger II production would start.
It was at this point Oberst Wolfgang Thomale (a higher-up in the Tiger program) stepped in and rejected this idea. He consented to September 1943 as the start of production of the Tiger II.
Tiger I and II and their Variants by Walter Spielberger