In addition to the battleships of the H-Class, a group of 12 new armored ships (Kreuzer P ), successors to the famous Admiral Graf Spee , Admiral Scheer and Lützow , were part of the Z-Plan. The design studies for the three battlecruisers of the O-class (Schlachtkreuzer O , Schlachtkreuzer P , Schlachtkreuzer Q ) were simultaneous started to those of the new Panzerschiff design (Kreuzer P ) in 1937.

In 1939 it was considered to replace three of the Panzerschiffe with the same number of this new battle cruisers. Construction orders were given to Deutsche Werke, Kiel, the Kriegsmarinewerft in Wilhelmshaven and the Germaniawerft in Kiel in the same year, but none of the ships were started.

Those ships were planed with the idea of commerce war in mind. Therefore, they should get a mixed propulsion system, diesel engines for long range medium speed cruises and additional turbines for high speed combat action.. The main task for this kind of battlecruisers was to engage enemy convoys and destroy transports and cargo ships.

But in difference to the heavy protected H-Class battleships, those battlecruisers had armor protection of a cruiser only. So it's very doubtful that one of this ships would have been able to attack a good protected allied convoy.

For more information, see Schlachtkreuzer O.