Planning for the Tiger II started as early as May 1941, a year before the Tiger I entered production. By the fall of 1942/January 1943, designers started work on a new heavy tank that would eventually replace the Tiger I. In January 1943, Hitler ordered the new Tiger to be armed with a long 88mm gun and have 150mm frontal armor and 80mm side armor. Front and side plates were to be sloped and interlocked, resulting in a design similar to the then-new PzKpfw V Panther (Sd.Kfz.171).It shared many components of the Panzer V Panther and Tiger II production began in January 1944 and ended in March 1945 with only 489 production vehicles.