The first German battlecruiser——was commenced March 1908. Four Parsons turbines were used, improving speed to 27 knots and reducing weight. Four twin turrets mounted 28 cm guns; although the two centre turrets were still placed one either side of the ship, they were offset so could now fire either side. The design was considered a success, but the cost at 35.5 million marks was significantly above the 1906 allocation. Light cruiser development continued with the  light cruisers, which were to become famous for their actions in the start of World War I in the Pacific. The ships were 3,300 tons, and armed with ten 10.5 cm rapid fire guns and a speed around 24 knots.  cost 7.5 million marks, and  6 million marks. Four  were produced between 1907 and 1911 at 4,400 tons and around 8 million marks each. These had turbines, twelve 10.5 cm guns as main armament, but were also equipped to carry and lay 100 mines. From 1907 onward, all torpedo boats were constructed using turbine engines.
How many years did it take to produce four light cruisers?
4