Wrong...wrong..wrong and wrong...Iowa...regardless of the tactical conditions.
Iowa's 16" 50 cal. did not have superior range to the Yamato's 18"/45 cal. In fact, Iowa's range is listed as 42,345 yards, while Yamato is listed as 45,960 yards. Yamato's muzzle velocity was 2559 ft./sec. compared to Iowa's 2500ft./sec. Weight of projectile is obviously different too, 3219lbs. for Yamato vs. 2700lb. for Iowa.
With regards armor, Yamato exceeds armor protection versus Iowa in all cases, deck, belt, turret faces, conning tower and bulkheads. However, Japanese armor steel is considered inferior to US steel, so, even with the additional armor, it's a wash.
Iowa's combination of an inclined belt, and a highly effective STS-steel shell plate outboard of the belt (which has just enough resistance to strip the AP cap off of an incoming shell) give her a slight edge in my opinion.
So where are the differences?
US damage control is vastly superior to Japanese damage control, the Iowas are considerably faster, more maneuverable, and possess considerably better gunnery radar. Optically, the Japanese had superior optical gunnery after 1943...but...after 1943, optical gunnery didn't matter nearly as much as having good gunnery radar...look what happened to Kirishima against USS Washington during the night battle at Savo. Japan's reputation for night battles relied heavily on close quarter combat, combined with superior torpedoes. By 1943, that ceases to be a dominant factor.
Yamato carried Mk 2, Mod 2 radar, which, in essence, was not a pure fire control radar.
This radar set was capable of search, but not range determination, due to "the lack of display units and a plotter, and a broader radiated beam." At best, these sets were capable of radar-assisted gunnery (in conjunction with the ships' other optical systems), but were in no way capable of true blind-fire control.
The Iowa carries MK 13, 3cm bandwidth blind fire radar, capable of range determination. This was proven by the US cruisers at the battle of Kula Gulf, when Cleveland, Columbia, Montpelier and Denver, sank the IJN DDs Minegumo and Murasame without ever physically seeing either of the ships, they were sunk completey by gunnery radar.
Finally, shells and rate of fire...
Japan's 18.1 inch shells were of the Type 91 variety...if they hit, yes, they did huge amounts of damage. If they missed and fell short, they were designed to travel through the water and impact the side of the target, much like a torpedo. This feature however, impaired much of the ballistics of the projectile. As a result, at long ranges, the shot groupings would be less concentrated than the 16"/50cal US rounds. US rounds had superb ballistics.
The Iowa's rate of fire is also superior, but not by much. In a 5 minute engagement, Iowa could put up 77 rounds versus 68 for Yamato, this coming predominately from reload times.
It should be noted that firing cycle (minimum time between shots at a 'typical' battle range) is calculated at the base loading angle, which for most ships was between 2 and 5 degrees elevation. In a long-range duel, elevation of the gun to a firing angle of 30-40 degrees would account for an decreased rate of fire. Iowa's guns elevated at 12 degrees per second. Most elevated at around 6 degrees per second. The U.S. Naval Technical Mission to Japan issued a report on Japanese ordnance which states that Yamato's firing cycle was 1.5 rounds / minute (i.e. 40 seconds) at maximum elevation. Maximum elevation is 50 degrees, and loading is performed at 3 degrees. This means that the barrel must travel through a total of 47 degrees down, be loaded, and travel 47 degrees back up to maximum elevation, for a total of 94 degrees of travel. Her barrels elevated at 8 degrees per second, meaning that 11.75 seconds would be spent in transit, leaving a total of 28.25 seconds (40-11.75) for loading.
One also has to consider that the US effectively figured out how to improve the effectiveness of their gunfire at range. Face it...flat trajectory gunfire doesn't sink ships...plunging gunfire does...making holes from above. This is precisely why HMS Hood was trying to close range against Bismarck, because she was less susceptible to flat trajectory fire, and was highly susceptible to plunging fire at range.
The US Navy worked out the ballistics and range tables for firing the Iowa's 16"/50 weapons with reduced charges (three charges instead of four) which would still allow for great range (given the 50-caliber barrel), but would also require greater elevation for a given range, and thus provide greater striking power against deck armor. In other words, fire with less powder at a higher angle, and lob the shells into the deck, historically, the weakest part of the structure. We can't underestimate the effects of gravity!!!
At close ranges, these guns fire their shells at very flat trajectories, and shells coming in at flat trajectories tend to ricochet. It's very tough to get any sort of armor penetration at obliquities above 70-degrees. This means that flat trajectory weapons don't start getting effective deck penetration until they are much farther away and their shells start coming in at a decent fall angle. The end result is that guns that have poorer ballistics make up for it (to a certain extent) at longer ranges against deck armor because they must fire their guns at higher elevations for a given range, and therefore loft their shells higher, and consequently hit decks with the benefit of gravitic acceleration from a greater height.
So, in the end, Iowa sustains damage, most likely from lucky hits if the range is beyond 25,000 yards...but Yamato is pummeled, holed, her machinery spaces destroyed, fire control is wiped out, and is completely blind after the engagement, regardless of the range. Time of day or weather doesn't play a factor, because Iowa can see in the dark, rain, or fog thanks to her gunnery radar. Lastly, although Yamato is BIG, only her turret faces were designed to be inpenetrable to any naval gun at that time...not the rest of her. In fact, in most of her vital spaces, Yamato is only slightly better armored than Iowa.
If you really want the nuts and bolts of this discussion, along with the hard data I've provided, you need to get access to the following:
John Campbell, "Naval Weapons of World War Two", ISBN: 0870214594
Nathun Okun's Extensive Armor Penetration data: http://www.combinedfleet.com/gunarmor.htm
And the following articles written by Mr. Okun, who is an armor and ballisitics expert for the US Navy.
MAJOR HISTORICAL NAVAL ARMOR PENETRATION FORMULAE© by Nathan Okun
TABLE OF METALLURGICAL PROPERTIES OF NAVAL ARMOR AND CONSTRUCTION MATERIALS©
MISCELLANEOUS NAVAL-ARMOR-RELATED FORMULAE ©
Hope that answers any questions...I'll be more than happy to debate this topic further if anyone wants to!!
Best Regards,
Jeff Herne