on the sides, with a small section at the base of the small gunnery control tower, which stood atop the main conning tower. Campbell also provides a thickness of 17 cm for the main tower roof. The rear conning tower was less well armored; its sides were only 20 cm thick and the roof was covered with of armor plate; all three sources concur on the aft tower. Modifications The four Königs received relatively minor modifications in their short service lives, all made between mid-1916 and late 1918. The first three ships had their fore masts replaced with the same tubular mast that Kronprinz received as completed. After the Battle of Jutland revealed the danger that dislodged anti-torpedo nets posed to the ships' screws, they were removed. They also had most of their low-angle 8.8 cm guns removed and their firing apertures plated over. König and Grosser Kurfürst retained two of those guns and the former had her anti-aircraft guns replaced with four low-angle mounts in 1918. Markgraf only had two of her low-angle guns removed in 1917, while Kronprinz retained hers for the duration of the war. Another pair of 3-meter rangefinders were installed in the forward- and aftmost main battery turrets, and later in the war, these were replaced with rangefinders. An improved C/15 version of the Bg-Mittler system was installed, and Kronprinz and Grosser Kurfürst received an C/16 gyroscopic stabilizing system for the main guns, which improved accuracy by accounting for the roll of the ships and changes in gun elevation as they moved through the water. König was to have received one as well, but it does not appear that she did, while Markgraf had an improved C/17 version installed. Construction Service history After the start of the war in July 1914, work on the vessels was accelerated so they would be available for operations as soon as possible. König and Grosser Kurfürst were completed in the first weeks of World War I; the latter had completed sea trials in time to take part in the Raid on Yarmouth on 3 November 1914, as part of the High Seas Fleet, which provided distant cover to the battlecruisers of I Scouting Group that carried out the raid. Grosser Kurfürst participated in the raid on Scarborough, Hartlepool, and Whitby on 15–16 December, again providing distant support to the battlecruisers. Grosser Kurfürst, assigned to III Battle Squadron, formed the