All of the modern USN Battleships used a Skeg arrangement, North Carolina and Iowa used a skeg on the inboard shafts and the SODAK's on the outboard shafts. This had several possible advantages in protecting shafts, propellers and rudders, as well as strengthening the hull in a location where depth is not possible. The outboard skegs were tried in SODAK to avoid some of the severe vibration that the NC's had at high speed. The longer hull form and the same four/five blade prop scenario seemed to reduce this in the Iowa's to a satisfactory level.
The Iowa's were mostly a 33 knot SODAK, with similar armor and underwater protection and a considerably more effective 16" 50 cal Mk7 light weight gun. The Washington, though on paper not as effective ship, got her licks in first and devistated her opponent in short order. Good fire control! Shots that don't hit don't count. There was a possibility at Leyte that an Iowa and Yamato might have come to blows. Though the 18.1" rifles on yamato threw a larger shell, Iowa etc had a heavy shell with a higher sectional density and at least as good penetration capacity, higher speed, better manuverability and superior long range fire control. The old saying goes, "if you are in a fair fight you screwed up".
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