JOHT: Battlecruisers

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The Joy of High Tech

 

by

 

Rodford Edmiston

 

 

Being the occasionally interesting ramblings of a major-league technophile.

 

 

Please note that while I am an engineer (BSCE) and do my research, I am not a professional in this field. Do not take anything here as gospel; check the facts I give. If you find a mistake, please let me know about it.

 

 

 

Battleship vs. Battlecruiser

 

 

 

 

As an engineer I know the importance of the correct usage of terminology. One of my pet peeves is the casual use of technical words, especially when they don't mean what the user thinks they mean. Nearly half the times when some person unfamiliar with naval history uses the word "battlecruiser" the subject is a proper battleship. Often the person seems to think that a "battlecruiser" is some sort of superlative, indicating something more potent than a mere battleship. (Hey, it's a bigger word. It must mean something more, right?) Most of the other half of the times the term is used, they mean an actual cruiser, or some other class of craft smaller than an actual battlecruiser or battleship. Regardless, they are referring to something other than an actual battlecruiser. (I've even heard people use "battlecruiser" to refer to the Yamato and her sister ship, which were the largest battleships ever built. They were very, very definitely not battlecruisers.) Contrarily, most of the time when someone unfamiliar with proper use of military vessel terminology refers to a true battlecruiser, they use another word entirely. Perhaps even calling such a craft a battleship.

Part of the reason for this misuse of terminology is that relatively few battlecruisers were built and they only operated for a few decades. Of course, another part is that there has historically been a great deal of drift in naval military terminology, and far more widely than just in regard to battlecruisers. An original Torpedo Boat Destroyer was a small, fast, lightly armed ship designed to defend other fleet elements from attacks by torpedo boats (which can be considered early versions of the World War Two PT (Patrol Torpedo) boats). Today's destroyers are closer in size and function to the light cruisers of a century ago, usually with the addition of missiles. This change in use of terminology was primarily due to two factors: The development of technology and naval tactics through the decades, and politics. The Washington Naval Treaty of 1921 set limits on the sizes of ships of various classes, as well as the size of armaments such ships could carry. The London Naval Treaty of 1930 further split some of these classes, and included formal distinctions between light cruiser, cruiser and heavy cruiser. Things have continued to evolve since, but this column is concentrating on the first half of the Twentieth Century. Note that there is some overlap between battlecruiser and heavy cruiser, because they were designed for similar tasks. However, neither is a true battleship, and the heavy cruiser is generally smaller and more lightly armed than a battlecruiser from the same period. 

As time progressed the tendency was - and largely still is - for new ships in a class to be larger than their predecessors, with increases in both size and capability. Typically - though not universally - a heavy cruiser built for WWII is larger and better armed than a battleship built before the Great War, besides being faster. However, except for the fuzzy line between them and heavy cruisers, the distinction between what is and what isn't a battlecruiser is quite clear. It all boils down to the reason behind the concept.

The basic idea of the battlecruiser is simple: provide a ship with more punch than a cruiser and more speed than a true battleship. Speed enough for cruiser task force operations. Battlecruisers are less weakened battleships than they are strengthened cruisers. As originally proposed, these ships would be used with other cruisers for scouting, commerce raiding, engaging enemy cruiser task forces and making hit-and-run flank attacks in larger engagements, to harass enemy battleship task forces. They were supposed to use their superior speed to avoid direct engagements with true battleships.

Achieving this speed required starting with something the size - or at least the length - of a battleship, but with fewer main guns, smaller main guns, less armor protection, less range, or some combination. This to make room in a battleship-sized hull for enough machinery to push the huge vessel through the water at cruiser speeds. Designers of these vessels also commonly used a finer hull form. That is, the hull was narrower and therefore had less drag than a battleship of that length. Which meant that a battlecruiser had a smaller displacement on a hull the same length, so there was less room inside than for a similar length battleship.  

The first to put the idea into extensive practice were the British, but many other nations with large navies also built their own versions. As a rule, the British gave their battlecruisers the same guns as true battleships, gaining speed by sacrificing armor. The German battlecruisers, meanwhile, had true battleship armor and smaller-caliber guns. Other nations had other methodologies, and some even tried more than one variation. What unified these types of craft was achieving the goal of being faster than the equivalent battleships, and having heavier guns and armor than typically found on cruisers of the day. The high turn of speed let the battlecruisers select their engagements, either avoiding true battleships or making slashing attacks which provided the latter with little opportunity to respond during large operations (when they would be focused on enemy battleships). Meanwhile, their heavier guns provided a significant advantage over the armament of ordinary cruisers.

People who today discredit the entire concept of the battlecruiser ignore the fact that the type of ship was very successful when used as originally intended. When a battlecruiser squadron went against a conventional cruiser squadron, the latter lost. 

HMS Hood was the last of the British battlecruisers built for the Great War, not even being completed in time for that conflict. Once the British Navy realized the war would end before she was likely to launch, her construction was slowed and her three sister ships were cancelled. In large part this was due to the expectation of making design changes based on what was learned by the "failure" of the British battlecruisers at Jutland. 

However, the main problem at Jutland was that while British battlecruisers were made to run away from superior opposition, British Navy captains weren't. British battlecruisers had the size and guns of a true battleship, but couldn't take the same punishment. At Jutland battlecruisers fought with true battleships in the British line against German battleships. Three were consequently destroyed in very dramatic fashion.

The Hood was modified following this operation, both during initial construction and additionally during subsequent refits (on her final voyage she carried a number of civilian workers who were finishing the work of her last refit) but she still blew up very quickly and dramatically in one of the first major naval engagements of the Second World War, the Battle of Denmark Straight. To put it bluntly, she was overmatched, largely for political reasons. Additionally, the true lessons of Jutland simply hadn't been learned by the Admiralty.

There is more than the thickness and toughness of the armor to consider when evaluating how well a ship is protected. Even battleships only put their heaviest armor where it will protect vital areas: magazines, engine rooms and such. Other parts of the ship are less protected. The actual armor is within the hull, and has a shape only vaguely determined by the exterior shape of the ship. The internal armor layers are angled with respect to the expected path of incoming shells, which greatly increases the effective thickness. These angled walls of interior armor may also be intended to direct plunging fire - shells coming in at close to vertical from long range - back out of the ship.

As the Hood was slowly brought to completion her armor was upgraded. Claims were made when she was launched in 1918 that she was now a full battleship. However, that was only true if you considered older battleships. While the added protection was substantial, the improved portions covered less of her volume than was true on an actual, contemporary battleship. She was still fast, but because the added armor was not fully compensated for by weight reduction in other areas she was overweight her entire operational career.

Worst of all, there was little improvement in training those who tended the enormous appetites of the main guns. 

She should have done better at the Denmark Straights. The reason she didn't was almost certainly the same reason those earlier battlecruisers blew up at Jutland. To increase rate of fire safety measures in ammunition handling were bypassed. (Note that this is speculation, but expert speculation.) This left substantial amounts of propellant powder with an indirect path of ignition from a hit in the right spot. The Germans found the right spot. 

The US got a late start on building battlecruisers. Indeed, most of those she started or planned during the Great War were never completed. The Lexington and Saratoga were instead converted to aircraft carriers during construction. Interestingly, these Lexington class ships if completed as originally planned would have been closer to the later concept of the fast battleship than to the battlecruisers of other nations during the period. (Isn't it just like the United States to not only want it all, but to get it, no matter how much they have to spend?)

One supposed distinguishing factor between the classifications of battleship and battlecruiser is that the former can resist the effects of guns similar to those it carries, at least in the "citadel" where armor protection is concentrated. This is known as a balanced design. However, the resistance to shells depends more on the state of the delicate balance between offense and defense which exists at the time a ship is designed than it does on overall design philosophy. The Iowa class battleships had excellent armor protection, but would have been considered under-armored against an opponent with guns equivalent to their own. They were also very fast, as well as surprisingly maneuverable. However, the Iowas were true battleships. They just happened to have what were probably the best (though not the biggest diameter) large naval guns ever deployed. Those guns were very accurate (a full broadside at maximum range covered an area about the size of a football field; that's target rifle accuracy from nine separate guns acting together) had very good range and the armor piercing shells they fired were very good at their job. All due partly to this being the last battleship class built. Advancements in design due to lessons learned and to the improvements in the technologies involved greatly helped make the Iowas superb warships.

As the Second World War progressed, the jobs formerly assigned to battlecruisers were generally split between existing heavy cruisers and fast battleships, with the Iowas being excellent examples of the latter. Such vessels were made possible by a combination of a better hull form - which offered less drag - and new steam boilers and turbine engines which provided more power in less volume with less weight. (Note that the Iowas also had excellent safety measures for keeping flame from a hit away from exposed powder. Something which may have saved the Iowa herself when a faulty powder charge destroyed the inside of one of her turrets, on April 19, 1989.) With true battleships now as fast as cruisers, there was simply no need for the battlecruiser. If your cruiser task force needed a heavier punch, simply add a heavy cruiser or, for really deciding the issue, a fast battleship.

The battlecruiser as originally conceived made good tactical sense. It just happened that they were the best tool for the job for only a relatively short time.