In the one sense, the Iowas and Yamatos were dreadnoughts; after all, they had a homogenous main battery, with all guns of a single calibre, as well as speeds above 21 knots and significant armour protection. However, by the time of their construction, the term 'dreadnought' had generally been superseded.

The first dreadnoughts were defined by their differences to preceding battleships (pre-dreadnoughts). These had a mixed battery, with up to four slow-firing heavy guns (12in) as a main battery and a secondary battery of smaller, faster-firing guns, all used for fighting enemy battleships (6in-10in). Dreadnoughts, by contrast, were 'all-big-gun' ships, with a main battery of eight or more heavy guns. The secondary battery was reduced to a vestige, for protection against destroyers. Dreadnoughts, which used the newer turbine machinery, were also faster than the older ships. However, within a few short years, the dreadnoughts themselves were being superseded. The introduction of superfiring turrets carrying even heavier guns (13.5in-16in) created ships often called 'super-dreadnoughts'. The first such ships in the Royal Navy were the Orion-class, built in 1913. The superfiring arrangement was more efficient than the wing turrets used on the earlier dreadnoughts, allowing for more armour to be carried. The heavier guns, meanwhile, could do more damage from a longer range. This meant that super-dreadnoughts were superior to the dreadnoughts, albeit not to the same extent that the dreadnoughts were superior to the pre-dreadnoughts. This was why Dreadnought herself spent most of WWI with the pre-dreadnoughts of the 3rd Battle Squadron, rather than with the Grand Fleet.

However, the super-dreadnought was soon to be superseded by the 'fast battleship'. These had the same armament as the super-dreadnought, but were considerably faster. The first ships commonly thought of as 'fast battleships' were the British Queen Elizabeth class, constructed from 1912-1916. Unlike later fast battleships, these had a distinct tactical role envisaged for them. British tactical though in the pre-WW1 period emphasised the need for a 'fast wing' of the battlefleet. This would be a fast squadron that could threaten the front and rear of an enemy's line during a fleet action; either the fast wing would achieve a superior position relative to the enemy's line, or force them to manoeuvre such that they were an inferior position relative to the main British line. This role had originally been envisaged for the pre-dreadnought armoured cruisers. Once the dreadnought age rolled around, battlecruisers naturally took this role (see here more information on what a battlecruiser is). However, as the Germans began to build their own equivalents, exercises showed that the British battlecruisers would be too busy engaging them to form a fast wing. These exercises pointed to the need for the fleet to have its own 'organic' fast wing as an inherent part of it. The Queen Elizabeths were constructed to fulfil this role. They had a top speed of 25 knots, four knots faster than the typical British fleet speed of 21 knots, but three knots slower than the contemporary battlecruiser Tiger. They also had the same armour and armament as contemporary battleship classes, like the 'R's. As such, considering them 'fast battleships' as a distinct class makes perfect sense - they were an intermediary between the battleship and battlecruiser, both in terms of speed and role.

The next British ship that might be considered a 'fast battleship' is the Hood. The first designs for Hood (and her three cancelled sister ships) were along the lines of the classic battlecruiser. It would have 32 knots of speed, but only had an 8in belt (though this was fairly extensive, had an effective thickness increased by its slope, and was backed by a 1.5in shell plate). Her keel was initially laid down on the 31st May 1916. Other events occurring on the same day led to a major redesign. The explosions of three British battlecruisers at the Battle of Jutland were seen as discrediting lightly armoured battlecruisers. Instead, the Admiralty wanted thicker armour, at the expense of speed. Hood was redesigned with thicker armour protection than the Queen Elizabeths (the belt thickness was the same, but Hoods was sloped and again, backed by a 1.5in plate). Hood is often described as a battlecruiser, because that is how the RN classified her, and the tactical role she was used in. However, if we look at just her physical characteristics, the argument that she is a fast battleship becomes more clear. Some 33% of her displacement was armour, a greater percentage than any British battleship bar the King George V class of 1936. Her armour protection was equivalent to contemporary British battleship designs.

The immediate post-WWI period saw a profusion of battlecruiser designs that might also be considered fast battleships. The British G3 design is particularly notable, having the same armour and armament as the American Iowa class of twenty years later. However, the Washington Naval Treaty of 1922-3 brought an end to these designs. The building holiday enforced by Washington would be extended until 1936 by the First London Treaty of 1930. When it expired, most major navies constructed new battleships. All of these ships had speeds in the vicinity of 30 knots. They were also all indisputably battleships, built as the centrepiece of the battlefleet, rather than as a peripheral but significant element like battlecruisers. All the classes had thick armour, and heavy armament, making them physically battleships too. With their high speeds, they were much faster than the older battleships that made up the majority of the world's navies. As such, they are described as fast battleships. The Iowas and Yamatos fall into this group.