75 mm gun could penetrate the new Soviet tanks. Germany also developed the heavy Tiger I, released in 1942. The Tiger was soon joined by the Tiger II, also known as King Tiger, but too few were produced to impact the war in any discernible way. One note of interest was the poor reliability of the German tanks such as the Panther and Tiger; constant mechanical failures meant that German tank divisions were rarely able to field a full complement of tanks and were often diminished below 50% combat readiness. The book The Last Battle by Cornelius Ryan makes mention of the 7 million foreign workers who were forcibly brought into Germany to work in the factories and businesses --- many of them in military assembly lines. Ryan specifically writes about these foreign workers in German tank manufacturing, who sabotaged every part they could and may have contributed to the rate of breakdown of German tanks in the field. This especially affected tanks built later in the war (such as the Panther and Tiger) when forced labor had replaced German manpower in their manufacture. In the Battle of Kursk, when the newly arrived Panther tanks moved into their assembly areas, 45 out of 200 experienced mechanical problems requiring repair. A good example was the Großdeutschland Division, which had a brigade of two battalions of new Panther Ausf. D tanks come under its operational control before the battle. After the launch of Operation Citadel, the new Panthers were plagued by technical problems, suffering from engine fires and mechanical breakdowns, many before reaching the battle, in which the division was heavily engaged. Also, it may have affected the Großdeutschland Division's non-role in the ensuing epic tank Battle of Prokhorovka, in which it was held in reserve, its Panther tanks not engaging as most were broken down by the time the battle started. It also may have been an issue with the Tiger tanks. The Tiger's reliability problems were well known and documented; Tiger units frequently entered combat understrength due to breakdowns. It was rare for any Tiger unit to complete a road march without losing vehicles due to breakdown. The Jagdtiger, built on a lengthened Tiger II chassis, suffered from a variety of mechanical and technical problems and had frequent breakdowns; ultimately more Jagdtigers were lost to mechanical problems or lack of fuel than to enemy action. German factories and industry was