These "P-Class Panzerkreuzers" were meant to be an improved Deutschland-class "pocket battleship" for commerce raiding. On such a large ship (twice the tonnage of Deutschland), increased armament was sacrificed for heavier armor, additional bunkerage for endurance, and high speed. They would have been the heaviest "cruisers" or the weakest battlecruisers in the world (compare with the Netherlands' Ijsselmeer). A novel feature was the "transom" stern which, though squared off, "fools" the ocean into believing she's longer (quite common on modern Navy ships). Twelve of these ships were envisioned for the German Navy's "Z" Plan, but none were built, and the concept was dropped in favor of the "O-P-Q" battlecruisers.

In "Grand Fleet" the Posen is finished in 1937 but her sister Pommern, due out the following year, is converted to a new type of aircraft carrier on Göring's express orders. Both ships sailed to Southern waters just before hostilities broke out. A slow convoy escorted by British battleship Ramillies and a French cruiser was sighted and engaged by Posen. The new German 11" guns were superior in range and rate-of-fire to the British 15" guns and had the added advantage of radar-ranging. Ramillies was sunk, but as Superb was reported to be just over the horizon, Posen turned and fled. She attempted to run past Gibraltar into the Mediterranean with Hindenburg but was turned back by air attacks and limped into Brest. After repairing, she was present at the North Sea battle when Führer disintegrated. Surviving only because of her high speed, she escaped from that battle only to be caught two months later and sunk by HMS Duke of York.