Selecting F3 instead of O3 provides a counterfactual in which the Royal Navy builds a fast battleship capable of a proposed 28 knots. Shaft arrangements remain uncertain: the designs are often listed with two shafts, while faster proposals, especially F2, are interpreted as likely to need more to transmit their power. Four shafts are considered more consistent with Royal Navy practice than three. For the Illustrious-class carriers, accepting three shafts allowed the desired torpedo-defense subdivision to take precedence over a fourth shaft. That protection contributed to their survival under attack, although machinery trouble could make the three-shaft arrangement harder to manage.
Notable Point · 17:11-18:50
F3 and Illustrious show why shaft layouts were design compromises
The uncertain shaft requirements of F3 and F2 contrast with Illustrious's choice to preserve torpedo-defense subdivision at the expense of a fourth shaft.