Classes

I've been asked several times about classes. A class of ships is a group of ships all built to the same set of blueprints, at least in theory. As with most naval matters, things are more complicated. In some cases, members of a class are essentially identical, while in others, they're totally different.

Iowa, New Jersey and Missouri as completed

As you'd probably expect, we'll start with the Iowas. All four ships were built to fairly similar plans. The biggest structural differences are Iowa's three-level conning tower, intended to house an admiral and his staff in battle,¹ and the heavier armored bulkheads on the ends of the citadel in Wisconsin and Missouri. The most obvious external differences early on were in the bridgework. Iowa commissioned with an open bridge around the front of the conning tower, like the earlier battleships, while New Jersey entered service with a circular enclosed bridge wrapped around the front of the conning tower. Missouri and Wisconsin had a square bridge, which Iowa and New Jersey received during refits.²

The picture of Wisconsin I identified³

When reactivated for Vietnam, New Jersey received a distinctive structure high in the tower for ECM systems. This structure was reused in the 80s, while the other three ships all had very similar air-defense levels. The other differences are minor. There were often small differences in the antenna layout, and some of the fittings differed. I once was sent bow-on picture of one of the ships in the 80s, from an angle where no markings were visible. New Jersey was easily eliminated, due to the differences at the air defense level. I then took a careful look at the ventilators on the forecastle, and was able to eliminate Iowa because they added more in the later ships. I was then stumped for a while, but eventually realized⁴ that the very tip of the bow differed slightly due to the way they'd removed the Oerlikons, and nailed it down as Wisconsin. On a slightly less geeky level, when watching the movie Battleship⁵ I noticed that the ladders to the 05 level on Missouri were backwards relative to those on Iowa.

USS George H W Bush, the last unit of the Nimitz class

To answer the question more generally, some classes are nearly identical, while others are totally different from each other, depending on how they were constructed. Some of the mass-produced escorts of WWII were essentially built on an assembly line, and thus were practically identical. The Nimitz class, on the other hand, saw significant modifications for each unit, to the point that it's almost 10 distinct single-ship classes. This is reasonably common in classes built over a period of time, as improvements are made. Depending on the scale of these improvements, the resulting groups are often called subclasses or flights. And different yards just fit ships out slightly differently. In terms of fine details, it's normal for there to be enough difference among members of a class of battleships to be able to tell them apart in photos.

Three different versions of the Gearing class destroyer: Original, FRAM I, FRAM II⁶

The situation gets more complicated when refits enter the picture. Even leaving aside cases in which a ship is converted to do something totally different from its original purpose, variations in equipment build up as ships pass through the yards.

There's not a simple answer to questions of this type, unfortunately, but hopefully everyone is now confused on a higher level than they were.