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Cage Masts

In referring to great developments in ordnance, it is well to bear in mind that not only had the power of guns been greatly increased but the accuracy of fire was vastly improved due to greater training of personnel and greater precision of instruments and methods of obtaining ranges. It is interesting to note, in this connection, that at the end of the 19th Century four and five thousand yards was considered a considerable battle range, and just prior to the outbreak of the Great War 10,000 yards was considered a long battle range. The Battle of Jutland, however, was begun at a range of 20,000 yards, and the range was maintained at that approximate figure for a considerable period. The number of losses of vessels and great damage to vessels through long-range gun fire during this battle give convincing proof of the great strides which have been made in the development and operation of ordnance material.

The Royal Navy's foremost proponent of these fire control improvements was Percy Scott. He is generally credited with having been the inspiration and possibly mentor of the US progressives. By the early 1900's, a group of progressive US naval officers, most notably William Sims and Bradley Fisk, began to do a great deal of developmental work in naval gunnery and fire control. Realistic target practice was instituted, from which it was discovered that it was impossible to spot the fall of shot at the increased battle ranges which modern guns allowed, and that it was also nearly impossible to plot course, speed, bearing, etc, of opposing ships under way, which were trying to avoid being hit.

These problems led to two major improvements, salvo firing, whereby several guns of the same caliber attempted to fire at the same time, blanketing a target with overwhelming explosive power, and director firing, a centralized means of plotting the variables of naval gunnery, and electrically aiming and firing the guns from one place, at one time, by one officer. New battleship designs and operational concepts featured uniform main battery large enough to blanket an opponent with a salvo, the need to be able to function at battle ranges of 10-12,000 yards, the need for some mechanical computation devices to plot battle variables of range, course and speed, and to tie it all together, some means of reliably seeing what needed to be seen, and the ability to transfer that visual information to the fire control officers.

The answer to this requirement was to raise the upper platform high enough above the waterline so a spotter up there could see to the horizon 12,000 yards away, and to be able to compute range and bearing, and transfer that information down to fire control. All this required very sophisticated and delicate optical equipment. It was found that mounting this equipment on normal masts was very unsatisfactory. The mounting was not rigid enough, and conversely, the shock and vibration of firing the main battery seriously upset the instruments.

The Royal Navy solved this problem by using large tripod masts supporting heavy director tops. The Dreadnought appears to have the first of these, probably made possible because she was so much bigger than her contemporaries.

The answer was different in the US Navy. Cage Masts were found on every battleship built in the USA from about 1910 to 1920. Cage Masts are seen on many of the battleships, like the USS Tennessee, at Pearl Harbor. The cage mast was designed to allow spotters to direct artillery fire as at the time artillery fire was directed by eye sight. The cage mast thought to offer a variety of advantages. It provided the maximum reasonable height for gun spotting, which was important before radar. They were light weight, relative to British tripods. Cage masts were thought to provide better cushioning for shock damage caused by the firing of big guns. The cage mast had too little mass to detonate a major shell, and a small shell would only take out a few of the wires of the cage. This cage structure was designed to take multiple direct hits from enemy fire without collapsing.

One drawback to this design was its flexibility, which gave the spotters a wild ride in heavy seas or when the guns were fired. The cage mast themselves proved to have aerodynamic problems, did not prove to be all that strong, and sang in a stiff wind. One, on the USS Michigan, collapsed in a strong wind. According to one account, these new cage style masts were designed by naval designer Richard H. Robinson, but this is otherwise un-attested. Test firing made on the hulk of the San Marcos fitted with one of the new masts anchored in the Chesapeake Bay proved that these new style masts could take several hits and still stand.

Michigan and South Carolina were the first US dreadnoughts capable of fulfilling all the requirements enumerated above, and were built with cage masts. When the Great White Fleet returned from its around the world voyage, its ships were quickly equipped with cage masts, so they would at least look up-to-date, and could perform some portions of modern gunnery. Cage masts continued to be applied to the US battlefleet, (battleships, and the abortive battlecruisers) for all the ships constructed or planned before the Washington Arms limitation agreement.

The switch from pole masts to cage masts was based on a flawed theory that the cage mast, with 24 sets of oppositely "twisted" pipes, would be stronger and able to withstand shellfire. The collapses of masts in the 20s put this theory in doubt, and the case was closed during the "treaty drawdowns" which saw older ships, often with cage masts, being demolished in target practice - with the cage masts collapsing due to damage and their older military mast counterparts taking slightly more punishment before failure. The answer was the tripod mast which first appeared in the mid-20s on BB refits.

By the time North Carolina and Washington were designed, radar was contemplated and purely optical battle observation was less critcal. Many of the existing 2nd generation battleships were equipped in the 1930's with director firing for almost all of their gun batteries. These were combined and housed in very large and heavy tops, which were much too heavy for many of the old cage masts. Hence, Arizona, and many of her sisters, were fitted with tripod masts. A few of the more modern 2nd generation ships, some of the Marylands and Californias, for example, carried their cage masts through WW II.

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Page last modified: 22-07-2011 17:35:17 ZULU