O Class Battlecruiser - Genesis: P Class Cruisers

Genesis: P Class Cruisers

Even with the completion of the two Scharnhorst class battleships and the construction of two Bismarck class battleships, the German Navy had fewer ships than other European navies. This led to a decision in 1937 to build ships to an improved Deutschland class design. After more than twenty designs were considered to meet the navy's specifications, one was chosen; it was designated as cruiser "P" (the "P" for panzer — German: "armor"). Under the original plan, twelve P class ships were to be built. The ships were designed as cruiser killers that would have heavy enough armament and armor to take on light and heavy cruisers but enough speed to outrun battleships and battlecruisers.

Many problems were encountered with designing the ships, the most prevalent being armor. The required maximum speed of 34 knots meant that the minimum length had to grow from the original 217 m (712 ft) to 229.5 m (753 ft). It also meant that the beam could be a minimum of 25 m (82 ft)—unless diesel engines, like those used in the Deutschland's, were desired; they would increase the beam by 2 m (6.6 ft). Unfortunately for the designers, the widened beam meant that an even longer hull was needed to maintain hydrodynamic efficiency. All of this complicated the armor arrangements, as more armor was needed to cover the longer length and widened beam. Eventually it was deemed that it was impossible to include diesel power on a 20,000-tonne (20,000-long-ton) displacement.

The switch to battlecruisers was the result of a proposal to up the main armament from 283 mm (11.1 in)/55 caliber guns to 380 mm (15 in)/47 caliber guns. Various reasons were behind this. Among other reasons, experiments showed that the smaller gun was "far less effective" than the larger gun, a class of twelve ships would have overtaxed the shipyards already heavily burdened with other ships, and the smallest guns on any foreign ship in service or under construction were more than 30 mm (1.2 in) larger than the 283 mm guns. The most persuasive argument for increasing the armament came in 1939, when Adolf Hitler denounced the 1935 Anglo-German Naval Agreement.