Why 28 knots could be enough for Montana

If the United States learned Yamato's true size, would Montana remain a 28-knot design?

Probably; 28 knots already exceeded Yamato, though modest lengthening or more power might target about 30 knots.

Knowing Yamato's gun caliber would probably also reveal its maximum speed of about 27 knots. A 28-knot Montana with twelve 16-inch guns would already be a useful opponent. A longer hull or more horsepower might raise the speed somewhat, perhaps toward 30 knots. The proposed response stops short of demanding Iowa's full speed.