Z51 shows the intended three-shaft diesel architecture

Z51 was built but never completed, making it a historical design rather than an invented paper engine room. Its planned plant used six 12,600-horsepower diesels on three shafts for 36 knots and about 5,500 nautical miles at 19 to 20 knots. The outer engines would handle cruising and steering, while four engines geared to the centre shaft supplied high-speed power. That architecture shows how Germany intended to combine efficient cruising with full destroyer performance once larger marine diesels matured.