Derfflinger and the speed required by the mission

The Derfflinger class was nominally a 26.5-knot design, with practical performance also affected by whether German ships could obtain high-quality Welsh coal. Against that opponent, a 24-knot battleship squadron with 15-inch guns could still fulfill the mission of blocking a move around the Grand Fleet's end until the main force engaged. A faster Queen Elizabeth would not necessarily gain the roughly three-knot margin needed to dictate engagement range, so the tactical return was limited. Pursuing more speed would have required additional size or reduced subdivision, neither of which was automatically justified by the expected threat.