From a David Weber post to Baen's Bar Honorverse dated May 29, 2008:

A comparative look at the BC(P) vs BC(L)

    The BC(P) was very much the initial, original wet-navy battlecruiser in comparison to the original wet-navy dreadnought-class battleship. As I'm sure you're aware, the British Invincible-class battlecruiser carried the same 12-inch guns as the Dreadnought, but carried fewer of them. She was designed to do to the existing armored cruisers what the Dreadnought was designed to do to pre-dreadnought battleships: overwhelm them with volume of fire while maneuvering to remain outside the effective range of their own secondary and tertiary armaments. The Dreadnought mounted 10 12-inch guns, had a maximum belt armor thickness of 11 inches, a maximum deck armor thickness of 3 inches, a secondary armament of 24 12-pounders (three-inch), and a speed of 21 knots, which gave her a clear three-knot speed advantage over the preceding King Edward VII and (technically) succeeding Lord Nelson-class. The idea was that with her speed advantage, she would remain at range and hammer her opponents with a 12-inch broadside 2.5 times heavier than theirs.

    The Invincible, on the other hand, was designed to deal with armored cruisers like the Blücher, although Blücher may not be the best example, since she was actually laid down after the Invincible as a counter to what the Germans thought (as the result of some cunningly misleading "intelligence") Admiral Fisher was up to. The Scharnhorst would probably be a better example, since she was laid down in 1905, which makes her precisely what the Invincible was intended to kill when she was laid down in 1906.

    Scharnhorst's armament consisted of 8 8.2-inch guns, 6 6-inch guns, and 20 24-pounders. Her maximum speed was supposed to be 22.7 knots (that's what she made on her full-power trials), although it probably was 21 knots or less (probably considerably less) under normal operating conditions (accounting for sea state, fouling, etc.). Her maximum armor belt thickness was approximately 6 inches, her armored deck protection was a maximum of 2 inches, and the maximum armor over her main battery was 6 inches. Invincible, on the other hand, was designed for a speed under normal operating conditions of 25 knots (whether she could attain it under those "normal" conditions is debatable), and she was actually slightly larger than Dreadnought (by about 40 feet in length and about 200 tons displacement at designed load draft). Her horsepower was about twice that of the battleship, and she had a finer hull design, all in an effort to gain just 4 knots more speed. In addition, she sacrificed one entire main battery turret (giving her only eight 12-inch guns), her maximum belt thickness was only 6 inches, and her maximum deck thickness was only 2 1/2 inches.

    (Some of the same costs in an effort to secure greater speed can be seen in the South Dakota and Iowa designs. In effect, it cost 10,000 tons and a radically modified hull form to give the Iowa speed advantage of only five knots, without any significant gain in firepower. The Montanas, were designed for a speed of only 28 knots, roughly that of the South Dakota, but carried 33% more main battery firepower --12 16-inch guns, as compared to nine -- and a 16.1-inch main belt as compared to South Dakota's 12.2-inch main belt. Of course, her full load displacement was projected to be 70,965 tons compared to South Dakota's full load displacement of only 42,782 tons and Iowa's designed full load displacement of 56,270 tons. This is one reason I've always tended to think of the Iowa more as the battlecruiser to the Montana's battleship. It's also the reason the U.S. Navy always saw the Iowa as a specialist type, specifically designed to escort carriers.)

    When the battlecruisers were used in the role for which Admirable Fisher had originally envisioned them, they were completely successful. In fact, Invincible and Inflexible were involved in the Battle of the Falklands in December of 1914, and the Scharnhorst was one of their German victims. So long as no one else had battlecruisers, Fisher's design concept clearly had at least some validity. But once other people, especially the Germans, started building battlecruisers, the "speed is armor" argument Fisher had made -- that with their clear speed advantage over any opponent, his battlecruisers would be able to hold the range open against inferior-armed opponents and run away from opponents with superior armaments -- became far less applicable. Moreover, the Germans never really saw the battlecruiser as the armored cruiser on steroids so much as they saw it as a heavily armored unit designed to stand up to major-caliber fire and protected accordingly. (This undoubtedly owed a great deal to the fact that British naval concepts and designs were optimized for worldwide blue water deployments, whereas the Germans designed their battle fleet primarily for the sheltered waters of the Baltic and the North Sea. Especially under the visibility conditions which frequently obtained in those waters, it was much more likely that their battlecruisers were going to encounter enemy capital ships at relatively short range, and they designed them accordingly.)

    As the main armaments of the battleships grew heavier, their battlecruiser counterparts also had to gain in size and weight if their armaments were to keep pace. But to justify the entire battlecruiser concept, they had to maintain a speed advantage over their battleship contemporaries. They were now seen as the high-speed scouts of the battle line, designed to close with the enemy, cut their way through light screening forces, and then maintain contact with the enemy battle line while directing their own battle line into the most advantageous position before engaging. Obviously, this required speed, firepower, and armor, but you couldn't maximize all three of those qualities in a reasonably sized vessel. The Lion-class battlecruisers, laid down in 1910 [well, actually November 1909, May 1910, and March 1911), only four years after the Invincible, were better than 1.7 times the Invincible's size (29,700 tons compared to 17,370 tons) and theoretically good for two more knots speed, with 13.5-inch guns. That made them 4,000 tons bigger than the Orion-class battleships (which mounted the same caliber of main armaments, but carried 10 of them compared to the Lion's eight), but her maximum belt thickness was only 9 inches, 3 inches thinner than the battleship's and (considerably more ominous) 2 inches thinner than Seydlitz's (laid down 1911) and 3 inches thinner than Derfflinger's (laid down January 1912). Although her guns were considerably heavier than her German counterparts', her armor protection was inferior (and just looking at armor thickness actually understates the degree of inferiority, given the German ships' greater internal subdivision), and she had no significant speed advantage over them. Tiger (laid down June 1912), which was the first battlecruiser to use "small tube boilers," was capable of 28 knots, but carried the same armament and armoring scheme, and while the Renown-class ships (laid down January 1915) were capable of 30 knots, they paid for it with only a six-inch belt (in other words, the same thickness as Scharnhorst's) and carried only 3 15-inch turrets each. You don't even want to get me started on the Courageous and Furious classes' many absurdities.

    In other words, the compromises inherent in the battlecruiser design, at least as initially envisioned by Jackie Fisher, were fatal if they had to engage against properly designed and handled capital ships, and that is precisely what their doctrine and function had evolved into by the time of the Battle of Jutland. The Germans and the Japanese were closer to on the right track in their emphasis on armor, especially given those changes in doctrine and function, and their designs eventually evolved into the so-called "fast battleship." HMS Hood was a sort of transition stage, although she was far better protected than the pre-Jutland British battlecruiser designs, her armor scheme was obsolete compared to that introduced by the Americans in the Nevada and subsequently adopted by virtually all warship designers.

    I've gone into this detail not so much to impress everyone with my vast knowledge of obsolete warship types, but because of the parallels between the podnaughts and their battlecruiser counterparts.

    The BC(P) is essentially the Invincible. The type is capable of beating the bejassus out of any pre-pod design (including superdreadnoughts, if her pods are loaded with Mark 23 MDMs rather than Mark 16s), but it is inherently fragile, totally unsuited to surviving the sort of massed MDM salvos which can be thrown by SD(P)s, and short on combat endurance because of the lower number of pods she can carry. The BC(P) is not a disaster waiting to happen, but it is a type which must be operated within a clear understanding of its capabilities and limitations. It is not a generalist, and making the BC(P) bigger to address its limitations would not make it significantly less fragile and would cost it at least a portion of its acceleration advantage over other types. For picketing forward star systems, commerce raiding, screening heavier podnaughts, use against anything below the wall, etc., it is a highly effective type. For actually defending crucial star systems against attack by any opponent with SD(P)s or going toe-to-toe against a system-defense built around MDMs and a Moriarty-style fire control system, it is not a particularly effective type. It may well manage to get the job done, but probably at the cost of heavy damage and casualties and not cost effectively compared to doing the same job with wallers.

    The BC(L) is much more like the Kongo or even more like the Iowa-class battleships, although they also have their similarities to the Alaska-class CA(L)s. The Iowa-class's main belt armor had a maximum thickness of 12.2 inches, sloped at 19° the Alaska's maximum belt thickness was only 5.5 inches. The Iowa carried nine 16-inch guns; the Alaska carried nine 12-inch guns. Their maximum speeds were roughly equivalent, but the Iowa was clearly the tougher customer, and in that respect the Nike is an Iowa, not an Alaska. Without the hollow core of a pod-layer, Nike is structurally far tougher and stronger than an Agamemnon. She is also much more heavily armored (including, deliberately, in this "armor" category her active defenses, as well). She actually has the toughness to stand up under reasonable amounts of SD(P) fire, and she is only marginally "slower" than Agamemnon in terms of acceleration capability.

    Where Nike most closely resembles the Alaska design concept is that her designers deliberately stayed away from three-stage MDM capabilities. One of the big weaknesses of the original battlecruiser design (I'm speaking here about the Invincible) was that when you put battleship-sized guns onto a ship the size of the battleship, sooner or later it was going to be used as a battleship, whether that was its designed function or not. That's one of the things which has happened to the Agamemnon on more than one occasion, and the fact that there are never going to be enough hulls to go around means that the need/temptation to utilize a ship capable of carrying MDMs to do just that is probably going to be irresistible upon occasion even when the admirals in question know that isn't really what the ships were designed to do. With the Nike, that simply can't be done. You can't fire all-up MDMs from her, no matter what you do, so the pressure to force her into that misapplication of the type is much lower. Mind you, there will still be cases of "needs must when the devil drives," and the toughness of the Nike design will undoubtedly stand the BC(L) in good stead when that happens. Also, although you haven't seen it in the books yet, the Mark 16's laser head is slated for significant improvement, which will give the weapon more punch against heavier opponents. Even then, however, the fact that Nike is armed with Mark 16s is going to force them to be employed much more in line with the doctrine for which they were originally designed.

    Essentially, the BC(L) is envisioned by the Royal Manticoran Navy as the minimum platform capable of performing the traditional battlecruiser roles of long-range, extended patrol; long-range interdiction; construction of commerce raiders (not necessarily the same thing as convoy protection); flag showing and rear area security missions; screening heavier ships and critical convoys; and force projection against anything "below the wall," in an era of multidrive missiles. By pre-First Havenite War standards, they are huge, expensive units; compared to a current Manticoran SD(P), they are an austere, extremely economical means for projecting the required capabilities, which means they can be produced in sufficient numbers to meet the operational needs of the Navy.

    There are still aspects in which the Agamemnon type holds advantages over the Nike, and nothing I've said here should be taken to mean that the Royal Manticoran Navy regards the BC(P) as some sort of deathtrap. The type is , however, increasingly recognized as a transitional type and as a highly specialized type which brings with it its own inherent frailties. As such, the majority of the RMN's officers probably share Honor's view that Nike, not Agamemnon, is the likely pattern for the future.

    Bear in mind, however, that the very thing which initially produced the Agamemnon type and then led to the evolution of Nike as its complement/potential replacement was the rapid pace of innovation in naval weaponry, doctrine, and tactics. Should that rapid rate of innovation continue, ship types which look like world beaters may end up losing their primacy much more rapidly than some readers expect. Of course, sometimes that's because the readers' expectations are initially unrealistic. I would point out the example of the new LACs. As people like Alice Truman and Honor Harrington recognized all along, even the Shrike would be of limited utility against a capital ship which knew it was coming. Some readers seem to have missed the fact that the LAC's proponents, by and large, always recognized that, and that the screening, system patrol, commerce protection, scouting, etc., portions of LAC doctrine were developed in direct parallel with the strike portion of the syllabus for precisely that reason.

    I hope that hasn't muddied things up too much more in my pursuit of clarification. [G]