Seacoast Artillery Fuzes - yimg.com

Volume 12, Issue 3

The Coast Defense Study Group Journal

Page 32

Seacoast Artillery Fuzes Bolling W. Smith A fuze is a device in a projectile that causes it to explode. Although spelled both fuse and fuze, the army eventually standardized with the spelling fuze to distinguish between artillery fuzes and other fuses. Fuzes detonate on the basis of time, impact, or a combination of the two. The requirements for fuzes are simple, but exceedingly difficult. First, the fuze must be completely safe. That is, it must not act prematurely, neither when the gun is fired nor even if the projectile is dropped or struck. Interestingly, even if the fuze fails, the projectile will not normally explode until several yards from the gun; explosions within the gun are usually caused by defects in the shell rather than the fuze. Secondly, the fuze must be certain, that is, it should always detonate the projectile at the desired place or time.(1) Fuzes for Back Powder Shells As recently as the middle of the 19th century, artillery fuzes were relatively insignificant, especially for seacoast artillery. Most projectiles were solid shot, the few exploding projectiles were primarily from mortars and howitzers, not normally used against ships. In the 19th century, however, the advent of the shell gun began to change this, as explosive shells became common seacoast weapons. Guns could now fire shells containing black powder. These shells, if they exploded, damaged the enemy by the force of the explosion. Fuzes exploded either by impact or by time. Either posed problems; impact fuzed shells tended to bury themselves in the ground before exploding, and time fuzes were notoriously inexact. To aggravate the problem, black powder was a low order explosive, tending to break the shell into a few large pieces rather than a greater number of smaller pieces. Case shot, equivalent to shrapnel, was designed with metal balls and a small bursting charge which exploded before the target was reached, dispersing the balls to continue on and strike with the kinetic energy provided by the original projectile. Despite thickening around the fuze hole, the fuze was still a point of weakness in the shell, and it was essential that it be pointed away from the powder, to prevent it being driven into the shell, which would then explode prematurely, to the considerable discomfiture of the gun crew. The normal method for round shot was to strap a cylindrical block of wood, or sabot, to the shell before it was placed in the bore. The fuze was ignited by the flame which passed around the shell in the smoothbore gun. The earliest fuze was the time fuze. The originals were conical pieces of wood, bored all or most of the way through their length. The hole was filled with compressed powder, which in theory burned at a relatively constant rate. The gunner cut off the fuze or bored a hole in its side at the point representing the time the fuze was to burn.{fig. 1} This was relatively effective, but neither simple nor terribly accurate. An improvement was a wooden plug, bored out to accept a compressed powder charge in a paper case. This was safer and more certain, but still had several defects. For seacoast use, the most serious drawback was that ricocheting on the water could put out the fuze. For this reason, this simple fuze was largely replaced before the Civil War by the more sophisticated United States seacoast fuze, although the Confederates mostly used the earlier model.

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Fig. 1-Wood time fuze. Warren Ripley, Artillery and Ammunition of the Civil War, p. 273.

The U.S. seacoast fuze, designed for use in columbiads and other heavy weapons, had a brass plug forced into the fuze hole, like the wooden one. The fuze proper fit inside the brass tube. These fuzes burned 10, 14, or 20 seconds to the inch, using different compositions that were color coded for easy identification. The brass plug was threaded for a “water cap,” a circular brass disk with loose powder in a circuitous path to the fuze. Below the fuze, in the shell, was a lead safety plug, which prevented the shell from firing, even if the fuze was accidentally ignited, until the plug was dislodged by the firing of the gun.{fig. 2} Although the variety of guns and ammunition used by both sides during the Civil War produced an similar variety of fuzes, the U.S. seacoast fuze remained the principal fuze in American coast defenses. Another approach appealed to artillerymen. If a shell could be exploded on impact, it would eliminate the often inexact estimation of the range and time of flight necessary with time fuzes. This seems simple, but in reality posed serious difficulties. First, the fuze had to be “bore safe,” that is, it had to withstand the shock of firing. Needless to say, for artillerymen, bore safety was a matter of considerable personal interest. A second problem plagued smoothbore guns. Since the shells were round, there was no guarantee that the fuze would strike first. This problem was never effectively solved until the advent of rifled artillery.

Fig. 2-U.S. seacoast fuze. Ripley, p. 274.

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With the rise of rifled artillery during the Civil War, artillerists finally had projectiles which would always strike point first. Two types of fuzes were developed: percussion fuzes were inert until impact caused them to fire; concussion fuzes ignited on discharge, but the flame was kept from the bursting charge until impact. Both types were used, neither completely successfully. Combination fuzes, which exploded by either time or impact, were also used, although again in limited numbers. In a few instances, Confederates even used base fuzes against Federal ironclads. All in all, however, fuzes were not major items for seacoast gunners. Solid shot was preferable, especially for the Confederates, who had to contend against Union ironclads. Fuzes and exploding shells were more commonly used in the field and against fortifications.(2) Following the Civil War, for the next thirty years the principal weapons of the coast artillery were muzzle-loading smoothbore Rodman guns and muzzle-loading rifled guns converted from smoothbore Rodmans. The principal ammunition for both was solid shot, intended for use against ironclad warships. These did not require fuzes. Case shot continued in service, however, intended for use against small boats, and exploding shell was used against unarmored or lightly-armored ships. In 1887, the Ordnance Board tested an Armstrong combination point fuze in an 8-inch gun. The time firing was excellent, but the percussion mechanism was insufficiently sensitive. A safety feature which attracted the attention of the board allowed the cap and time igniter to be inserted in the fuze after the shell and fuze were already in the bore, adding to the safety of the gun crews.(3) By 1891, improvements in place, or foreseeable, in artillery demanded improved fuzes. As velocities and range increased, longer fuzes were needed. Increases in range also increased the difficulty of observing the range of the burst, and the increased velocity magnified the significance of small errors in time. The fuzes of the Civil War remained in service, with some small improvements. The point-mounted time fuze used an “inertia igniter,” since breechloading guns could not ignite the fuze through the windage, as did smoothbore guns. The inertia igniter used a pellet of fulminate suspended above a sharp point by either a spiral spring or a brittle pin. Either was designed to give way on the shock of firing, but not to any lesser force. The flame from the fulminate escaped through holes into a ring cavity, igniting the circular column of composition. The exterior of the ring was marked in seconds, and the ring was turned so that the desired portion of the composition ring was opposite the hole communicating with the shell interior. For longer ranges, two or more rings could be arranged, one atop the other.{fig. 3} For explosion on impact, both point and base fuzes were used. Point fuzes had the advantage that on impact the explosive was forced toward the fuze, but they so weakened the shell that they could not be used for attacking armor, necessitating base fuzes. Both Hotchkiss and Krupp fuzes were used, Hotchkiss making both point and base impact fuzes. In the point fuze, a lead plug, dislodged on firing, provided a safety factor. The plunger was forced back and held in place by brass wires until impact caused it to fly forward, striking the fulminate. In the base fuze, firing forced the lead plunger back on the firing pin, so that the firing pin point projected above the plunger. The firing pin being roughened, the plunger gripped the pin and on impact the plunger and firing pin together flew forward onto the fulminate. This design, while less certain than the point fuze, was the best available. Krupp also made a fuze in which a transverse pin was pushed aside by the rotation of the shell, allowing the firing pin

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Fig. 3-Frankford Arsenal combination fuze, 1891. ARCO, 1891, Appendix 19.

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to move forward on impact. This design was reported to be in the process of being replaced by one containing a safety device which was unscrewed by the projectile’s spin.(4) For armor attack, the Merriam base percussion fuze was finally perfected sufficiently for use in mortar shells. Mortars, the only breechloading seacoast weapons then in service, were a particular problem, since their relatively gentle shock of firing made it difficult to arm the fuze without making the fuze too sensitive for safety. A special feature of the Merriam fuze was a delay allowing the shell to penetrate before exploding. In the Merriam fuze, a heavy ball was kept in place at the rear of the fuze by small clips. The force of firing displaced the clips, freeing the ball. When the shell impacted, the ball moved forward, striking one of three small balls covering the fulminate caps and igniting it. For the delay element, a wafer of compressed powder was placed in front of the “valve.” When the valve was forced against the wafer, the powder burned relatively slowly, but when pressure on the valve was released, the wafer spread the flame rapidly. Thus the flame was delayed as long as the shell was retarded passing through the target, but fired quickly after passing through. By this ingenious means, the fuze adjusted automatically to the different resistances posed by the armored and unarmored portions of warships.{fig. 4}(5)

Fig. 4-Merriam fuze, 1893. Henry P. Merriam, “A New Percussion Fuze,” JUSA, Jan. 1893, pp. 59-65.

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By 1893, the Ordnance Department was beginning to test fuzes designed to detonate shells filled with smokeless high explosive. The near exhaustion of the supply of base fuzes offered the opportunity to produce fuzes with left-handed threads, which tightened when fired. These were produced in two sizes, .717-inch for shells under 5-inches, and 1.128inches for 5 inches and larger. In 1895, “Fuses for Field, Siege, and Seacoast Powder-Charged Shell and Shrapnel” was an appendix to the annual report of the chief of ordnance. Only two fuzes were listed for seacoast artillery, which had not really begun to appear in its new emplacements. The F.A. (Frankford Arsenal) point percussion fuze N, model of 1894, was used in 8-inch converted rifles, while the F.A. base percussion fuze A, model of 1894, was used in breechloading mortars. The model 1893 fuze A, of which about 550 had been made, was to be used up before the model 1894 was substituted, and differed only in minor details. When the model A base fuze was fired, the plunger sleeve slid to the rear against the safety ring, which was in turn pushed to the bottom of the spindle where a catch pin, actuated by a spiral spring, bound the sleeve to the spindle. The point of the firing pin then projected above the plunger sleeve, and the fuze was now armed. On impact, the plunger continued forward through inertia, and the firing pin pierced the primer shield and ignited the composition. The flame passed through two vents into the primer, and thence to a charge of rifle-powder and the bursting charge. The 1893 model omitted the catch pin and spiral spring, and a groove in the spindle held the sleeve and spindle together.{fig. 5}(6) Development of Base Detonating Fuzes In 1896 the Board of Ordnance and Fortification reported experiments with high explosive bursting charges for shells. What was needed was a base fuze able to detonate the high explosive, yet sufficiently insensitive to allow the shell to pass through the armor face before exploding. Eleven models of fuzes were tried, but none proved satisfactory.(7) Until 1897, experiments toward developing detonating fuzes for high explosive shells were conducted under the direction of the Board of Ordnance and Fortification, with no final result. From 1898 through 1901, however, considerable progress was made by Captain B.W. Dunn, building on the work of Captain W.S. Pierce, both of the Ordnance Department. By 1901, Dunn’s fuze gave general satisfaction. Initially, problems were experienced with a base cover for the base-mounted fuzes, but the inherent weakness of point-mounted fuzes effectively ruled them out, and on May 9, 1901, a satisfactory base cover was adopted.(8) In 1902, the chief of ordnance noted that the introduction of high explosive bursting charges for shells increased the importance of absolutely safe fuzes. There were two means by which this could be achieved, inertia and centrifugal force. Of the two, centrifugal force was preferred, since dropping the shell could result in considerable inertia, but under no circumstances could a shell be accidentally rotated over 2000 rpm. The first public test of detonating fuzes, conducted that year, concluded that “we now possess a detonating fuze unequaled for safety and efficiency.” Twenty thousand of these fuzes for siege and seacoast shell were being manufactured using fuze stocks on hand, while experiments progressed toward developing a cheaper and stronger stock for use with the fuze elements already developed. The design preferred for point fuzes was the “revolving pin fuze,” developed by Captain Dunn, in which the firing pin lay flat in the plunger, but was rotated into the armed position

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Fig. 5-M1893 and M1894 base fuzes. ARCO, 1895, Appendix 38.

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by centrifugal force when the shell was fired. A .02-second delayed action fuze cap was recommended for all future percussion fuzes. In it, a central hollow tube containing compressed mealed powder in front of the percussion primer was surrounded by rifle powder. A hole in the stem regulated the length of mealed powder to be burned before the rifle powder was fired, setting off the bursting charge.(9) For base percussion fuzes, a “centrifugal parallel movement plunger” was devised in 1903 by Mr. Matthew McBride, foreman of the fuse department. Meanwhile, the department settled on centrifugal fuzes for projectiles of 2.95-inch and larger. Three designs were developed. The “F” fuze was used in detonating stock already on hand. The “S” fuze plunger, which armed at between 2000 and 3000 rpm, was used in all projectiles except 12-inch mortar. The “12M” fuze, which armed at 1300 rpm, was used in torpedo detonating fuze stock on hand, but the plunger was not heavy enough, and a new design was being prepared, using a much heavier plunger. The “high C” ring-resistance fuze was issued as long as stock was on hand, after which it was to be replaced by the “S” fuze.(10) Ordnance Document No. 1727, Fuzes for Use in Mountain, Field, Siege, and Seacoast Powder-Charged Shell and Shrapnel and in Detonating Fuzes, written in 1904, was issued in 1905. It reemphasized that “the application of the Frankford Arsenal centrifugal fuze now embraces all projectiles above the 6-pounder in caliber.” The accompanying tables listed ring-resistance inertia fuzes only for field and siege guns and for 6-pounder shells. None of the centrifugal fuzes, the “F,” “S,” and “12-M,” were intended for use in seacoast ammunition, except for Pierce stocks tapped for 10,000 “S” and 2200 “12-M.” These stocks, with the newer fuze plungers screwed in their base, served until stronger, more modern stocks could be developed and issued. Three models of detonating fuzes were listed for seacoast ammunition. The special “S” fuze was a base fuze for 15-pounder high explosive shell; the “S” base fuze was for 8, 10, and 12-inch high explosive shell; and the “12-M” was a base fuze for 12-inch mortar torpedo shell. The “S” and “12-M” fuzes on hand were those converted using the older stocks. While older fuzes were illustrated and described, the only information published concerning detonating fuzes, other than the table, was their outside diagrams. The armor piercing detonating and torpedo detonating fuzes were termed “Pierce” fuzes, after the developer of their stock. The name continued to apply to the stocks, even after the plungers were repeatedly modified. With both the Pierce and the subsequent M1906 fuzes, the names applied more to the stock than to the internal workings, which were repeatedly upgraded.(11) By 1905, the centrifugal fuze was modified by the application of a device for insuring positive rotation of the plunger. According to the chief of ordnance, the centrifugal percussion fuze “. . .as now manufactured, embodies in a remarkable degree the elements that insure safety in handling and transportation and certainty of action.” The “lift link” centrifugal fuzes functioned by means of a link bar. When the halves of the plunger separated due to centrifugal force, the bar pulled the firing pin up to the armed position.{fig. 6} Experiments with detonating fuzes resulted in approval for manufacture of three sizes, for major, medium, and minor-caliber.(12) In 1906, however, the department sharply reversed itself. After asserting the clear superiority of centrifugal fuzes, the department reverted to ring resistance fuzes, stating “… the experience of the past year clearly demonstrated that the ring resistance fuze in projectiles insures a much larger percentage of bursts, both on direct and oblique impact, than the

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Fig. 6a.-F.A. centrifugal fuze “S,” 1904. Harold Cloke, The Gunner’s Examiner, p. 82.

6b.-F.A. centrifugal base fuze “12-M,” 1904. Mervyn Buckey, Manual for Mortars, p. 72.

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centrifugal fuze,” in addition to being simpler and cheaper. For seacoast artillery, only mortars retained the centrifugal style, due to their low acceleration when fired. The new fuzes, ring resistance for guns and centrifugal for mortars, were designated F.A. base detonating fuzes M1906.(13) By 1907, the Ordnance Department declared itself ready to supply detonating fuzes to the service in any reasonable quantity. Meanwhile, Lissak’s Ordnance and Gunnery repeated the 1902 arguments for the superiority of centrifugal fuzes over inertial ones, but noted that the centrifugal fuzes were only used for low velocity weapons, such as mortars; ring resistance fuzes being used with high-velocity guns. Again, all that was shown of the detonating fuzes was the outside. An article by Captain Schull shed a little more light on the detonating fuzes, noting that they were like the old style ring resistance and centrifugal fuzes used with black powder bursting charges, but contained a high explosive booster to detonate the high explosive filler. To contain the additional explosive, the bodies of the detonating fuzes had to be made considerably longer than the older fuzes, introducing additional problems of strength, especially in armor piercing shells. Ring resistance fuzes were divided into high and low versions, depending on the force required to arm the fuze. Low fuzes, intended for use in low velocity guns, howitzers, and mortars, were inherently unsafe, and had been replaced by centrifugal fuzes.(14) In 1908 the Ordnance Department revised and reissued O.D. 1727, significantly changing the portion on detonating fuzes. For 3-inch R.F. guns, 14,000 special “S” fuzes had been manufactured, but no more were to be made, as they had been superseded by the mediumcaliber base detonating fuze. The same was true for the 2100 “base detonating fuzes for minor-caliber projectiles,” for 3-inch field guns and 3-inch R.F. guns. These were not to be confused with “minor-caliber base detonating fuzes” for 6-pounder and 2.38-inch shells with picric acid bursting charges. The medium-caliber base detonating fuze was now to be used for all guns between 2.95 and 7 inches, as soon as the present stock was exhausted. For the four 4-inch Driggs-Shroeder guns, 292 special fuzes had been manufactured with split ring plungers, but no more were to be made. About 10,000 armor piercing base detonating fuzes (modified Pierce stock) were on hand for 8, 10, and 12-inch guns, and 3404 had been modified for use in 1046-pound deck piercing mortar shells. These were made by putting new plungers into the old “Pierce” stocks.{fig. 7} After this supply was exhausted, they were to be superseded by the major-caliber base detonating fuze. The 2200 torpedo base detonating fuzes (modified Pierce stock) on hand with the 12-M “lift link” design were to be used up and then replaced by the major-caliber base detonating fuze.(15) In 1909, the Ordnance Department again reversed itself after two years of tests, adopting the Semple centrifugal plunger.{fig. 8} The Semple plunger incorporated several safety factors. The firing pin pivoted on the pin J (see diagram), but pins H from each side of the plunger fit into holes in the pin, preventing its rotation. When the gun was fired, centrifugal force moved the pins, H, out of the way, unlocking the pin. While the shell accelerated in the barrel, inertial force prevented the pin from rotating. When the acceleration ceased, the pin rotated so that the point was forward, and when the shell struck the target, the pin was forced into the primer, which fired, setting off the booster, which in turn detonated the bursting charge. Mortar fuzes armed at 1300 rpm, while gun fuzes armed at 2000 rpm. Due

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Fig. 7-Modified Pierce stock, outside dimensions. O.D. 1727, 1914, plts 21 & 22.

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to their small size, the minor-caliber base detonating fuzes retained the ring resistance design. The designation of these M1906 fuzes with the new plungers remained unchanged.{fig. 9}(16) In 1913, O.D. 1727 was revised, and reissued the following year. Detonating fuzes were still considered secret; the text referring to table IV, noted “This table gives all the informa-

Fig. 8-Semple plunger. Earl McFarland, Textbook of Ordnance and Gunnery, p. 516.

Fig. 9a-M1906 base detonating fuzes, with Semple plungers. Paul S. Bond (ed.), The R.O.T.C. Manual, 1928, p. 36.

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Fig. 9b. O.D. 1727, 1914, plate 19.

tion to be published in connection with fuzes of this class.” Table IV itself was little changed from 1908. The 6-pounder and 2.38-inch steel shell now contained TNT. About 10,000 AP base detonating fuzes and 2200 torpedo base detonating fuzes (both modified Pierce stock) were still on hand. Major-caliber base detonating fuzes were now listed for all guns above 7 inches, including the 14-inch guns now being mounted and the one 16-inch gun not yet emplaced.(17) By 1917, the major-caliber base detonating fuze was replacing the Pierce armor piercing base detonating fuze for mortar shells; no more of the latter were to be issued after the present supply was exhausted. The major-caliber fuze was 6.7 inches long, while the armor piercing base detonating fuze was 9.5 inches long. The major-caliber fuze was used in mortars and guns of 8 inches or larger. Mediumcaliber fuzes were used for 5 and 6-inch guns, and minor-caliber fuzes were used for 3-inch or smaller. Fuzes for A.P. shot were delay action, allowing the shot to pass through armor before exploding, while shell fuzes were non-delay, except for deck piercing mortar shells, which used delayed action against ships.(18) During WWI, a new base detonating fuze was developed, the Mk. V. This centrifugal fuze used the Semple plunger without a delay element. It was bore safe and much more consistent

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Fig. 10-Mk. X base detonating fuze. Earl McFarland, Textbook of Ordnance and Gunnery, p. 530.

than the previous M1906 fuze. Since smaller shells, 10 inches and below, were no longer considered effective for armor penetration, the non-delay Mk. V was considered perfectly adequate for them. However, the Mk. V, with no delay, was unsuited for use in guns above 10-inch. Therefore, between 1923 and 1925, the Mk. X base detonating fuze was developed. It also used a Semple centrifugal plunger, with a delay element. Here, however, interchangability reared its ugly head. The openings in the shell bases for the M1906 and the Mk. V fuzes were the same. Although the dimensions of the fuzes differed, and the holes in the filler had to be changed, at least the fuzes were interchangeable so far as the shells were concerned. Not so with the Mk. X. Any shell base threaded for an earlier fuze had to be bored out to receive the new fuze, a time consuming task. In 1925, coast artillery ammunition reserves contained projectiles intended for no less than five different fuzes, posing a serious problem in terms of standardization. The plan was

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Fig. 11-Mk. V base detonating fuze. P.S. Bond (ed.), Military Science and Tactics, Senior Division, Coast Artillery, Basic Course, 1939, p. 27.

to use the Mk. V for smaller caliber shells, and older fuzes, principally the M1906, in larger caliber shells until Mk. X fuzes became available and projectiles were modified to accept them. At the same time, aluminum fuze liners began to come into use, eliminating the need to coat the fuze stocks with rubberine to prevent contact between the stock and the explosive fillers. Introduction of aluminum liners greatly eased the danger of the development of explosive salts, and facilitated the process of fuzing the projectiles. Shells only received liners when they received their permanent fuzes, however; those temporarily fitted with M1906 fuzes did not receive the liners.(19) The Mk. X fuze contained a Semple plunger, which fired a primer, which in turn set off a delay pellet. A 3/8-inch thick rotor disk lay above the delay pellet, and a detonator in the rotor swung into position between the delay pellet and the tetryl booster when the shell was fired, allowing the booster to be fired and to fire the bursting charge. The primer, with its plunger and rotor, was bore safe. It armed by rotation at 1300 rpm, allowing it to be used in either guns or mortars.{fig. 10} The Mk. V non-delay fuze was similar, but did not have a rotor. An centrifugally operated interrupter was placed between the detonator and the booster, making the fuze bore safe. Being non-delay, the Mk. V did not have a delay pellet. It was issued in both major and medium-caliber sizes.{fig. 11}(20) The Mk. IV base detonating fuze was used in minor-caliber guns. Unlike its larger counterparts, the Mk. IV fuze was operated by inertia, rather than centrifugal force, and it was non-delay. When the gun fired, the plunger moved rearward, shearing a pin. The plunger then became crimped around the firing pin, and on impact the plunger and firing pin moved forward together, striking and exploding the primer, setting off the detonator, and ignited the bursting charge.{fig. 12} By 1942, however, the Mk. V was used for 3-inch seacoast ammunition.(21)

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For mortars, both Mk. X and Mk. V base detonating fuzes were used, depending on whether or not a delay was desired. For 16-inch guns, the only base detonating fuze listed was the Mk. X. As early as 1942, M60 base detonating fuzes began to replace the Mk. X in 155 mm and smaller ammunition. Closely resembling the Mk. X, they also used the Semple plunger with rotor. For armor penetration, 90 mm AMTB guns used the M68 base detonating fuze. This was a ring-resistance, inertia-type delay fuze. The heavy plunger-type firing pin pushed against the base of the fuze, restrained by a resistance ring. On impact, the pin rode forward, shearing the ring and firing the primer. The fuze had a boattail projecting from the rear of the shell which contained a tracer element, which functioned independently of the fuze.(22)

Fig. 12-Mk. IV base detonating fuze. Thomas J. Hayes, Elements of Ordnance, p. 593.

Point Detonating Fuzes Although base fuzes were required for armor penetration, the coast artillery did not always need armor penetration. They also fired on unarmored ships, the unarmored portions

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of armored ships, and at land targets. For such targets, point fuzes were often used, although because they weakened the point of the projectile, they could not be used with armor piercing ammunition. Point fuzes were divided into impact, combination, and time. Impact, or percussion fuzes, were the most common point fuzes. In 1905, the only fuzes for high explosive seacoast artillery ammunition were base mounted. Base fuzes continued to be used until WWI saw the development of the Mk. III point detonating (PD) fuze. The Mk. III PD fuze was a super-quick fuze, exploding shells before they could bury themselves in the ground. It was used with high explosive shell from 155 mm to 12-inch. The Mk. III was a fairly complicated device, with several safety features. A brass spiral, wrapped around half rings at the head of the fuze, loosened when the shell began to decelerate after firing. When the spiral unwound, it freed the half rings. The only thing now preventing the firing pin from being forced back into the primer was the safety wire. An interrupter, placed between the upper and lower detonator, was held in place by inertia when the shell was accelerating in the barrel, but when the shell ceased accelerating, centrifugal force moved the interrupter out of the way, clearing the flame path between the upper and lower detonators. When the shell struck, the safety wire was sheared and the pin struck the primer, which in turn set off the upper detonator. This, with the interrupter out of the way, set off the lower detonator, which detonated the bursting charge.{fig. 13} The Mk. IV and Mk. IV-star PD fuzes were used when a delay was desired. The only difference between the two was that the Mk. IV-star with a stronger retard spring was used in guns, while the Mk. IV was used in 12-inch mortars. Although nondelay and long-delay (.15 second) versions were manufactured, they were discontinued before 1935, and only the short-delay (.05 second) version remained in stock. When fired, the arming casing compressed the arming spring and disengaged the safety casing from the percussion plunger, while engaging the collar of the percussion plunger. This exposed the percussion primer, arming the fuze. The retard spring prevented the plunger from creeping forward during flight. On impact, the plunger moved forward and exploded the primer against the firing pin. The flame from the primer passed to the powder pellet, to the delay pellet, to the relay powder, to the detonator. The detonator, approximately 30 grains of mercuric fulminate, detonated the booster, which detonated the shell filler. {fig.14}(23) Fig. 13-Mk. III point detonating fuze. Earl McFarland, Textbook of Ordnance and Gunnery, p. 518.

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Fig. 14-Mk. IV point detonating fuze. Earl McFarland, Textbook of Ordnance and Gunnery, p. 521.

During WWII, the Mk. III and Mk. IV PD fuzes continued in use, the Mk. III with 12inch mortars, the Mk. IV with 6 to 12-inch guns. They were, however, largely supplanted by improved versions, the M46, M47, M48, and M51. The M48, the best known and most widely used artillery fuze of WWII, was used in 3inch and 90 mm guns. It was quickly adjustable for either super-quick or .05-second delay action. The M48A1 and A2 had a .15-second delay.{fig. 15} The M51 fuze, composed of the M48 fuze with the appropriate booster, was the principal replacement for the Mk. IV-star. It also could be quickly adjusted to give super-quick or delay (.05-second) action. Later M51A3 and A4 versions provided a longer delay (.15-second). False long-ogive shells for 8-inch and 155 mm were fitted with a special fuze, the M51 Mod 3. This came with an extended flash tube reaching to the front of the ogive. If the shipping head was left in, the fuze had delayed action. For super-quick action, the shipping head was replaced by the usual super-quick element.{fig. 16}(24)

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Fig. 15-M48A2 point detonating fuze. Ohart, Elements of Ammunition, p. 153.

M46 and M47 PD fuzes were improved versions of the M35 PD fuze, which was in turn an improvement on the Mk. III PD fuze. The M46 was shorter, simpler, safer, had a more powerful detonator, and was more reliable. A light firing pin was supported on a brass cup sufficiently strong to resist the acceleration of firing. On impact the firing pin was driven through the cup. The only difference between the two was that the M46 was super-quick, while the M47 incorporated a .05-second delay pellet between the upper and the lower detonators.{fig. 17} Point-fuzed ammunition was not issued to guns above 12 inches.(25)

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Fig. 16-M51 Mod 3 point detonating fuze. Ohart, Elements of Ammunition, p. 170.

Fig. 17-M46 point detonating fuze. Coast Artillery Gunner’s Instruction, Fixed Seacoast Artillery, First and Second Class Gunner’s, TM 4-305, p. 193.

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Combination fuzes acted by either time or impact. They exploded either when they struck a target or if the predetermined time had passed. Combination fuzes were primarily used by field artillery, but they could be used with shrapnel by the coast artillery against troops, unprotected equipment, or unarmored vessels. In 1903, the Ordnance Department continued testing DuPont and Frankford Arsenal combination fuzes. By 1904, progress was being made in the development of combination fuzes. The first problem, igniting the time train, was successfully solved, but the burning times were still occasionally erratic over 10 seconds. Mechanical timers were also tried, but not yet successfully. While experimentation continued, 20,000 combination fuzes were bought overseas.(26) By 1907, the basic combination fuze used through WWII was developed. Different forms allowed 21 and 45-second intervals. The M1914 45-second combination fuze was very similar and was used along with the M1907, but did not replace it. In 1913, 1600 30-second combination fuzes were ordered for use in shrapnel for 6-inch Armstrong guns. In addition, a small lot of 70-second combination fuzes was made for testing shrapnel for 12-inch mortars. In 1915, shrapnel was issued for 4.72 and 5-inch seacoast guns used for land defense. The M1907 and M1914 were used with 155 mm shrapnel, and the M1907 was used with 3-inch seacoast guns. By setting the time ring for 0 seconds, the shell functioned as canister. The fuze could be also used simply as an impact fuze, by setting the time ring for either safe or for a time longer than the anticipated time of flight.

Fig. 18-M1907 point combination fuze. Earl McFarland, Textbook of Ordnance and Gunnery, p. 527.

The M1907 combination fuze contained two parts; the upper part contained the same powder train time element as the antiaircraft fuze, while the lower part contained the percussion element with a Semple plunger. Due to the sensitivity of the percussion element, the fuze came equipped with a safety wire, to be removed only when the shell was ready to be fired.{fig. 18}(27)

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Time fuzes were not often used by the coast artillery, but they were considered effective against high speed small craft, and 90 mm batteries were equipped with M43 mechanical time fuzes, with clock mechanisms.(28) Summary Fuzes, although prosaic, were important. In his Corregidor diary, Colonel Paul Bunker frequently mentioned fuzes. Super-quick or non-delay fuzes were essential against land targets. Mark III PD fuzes were effective with high explosive mortar shells, but were in short supply. In an attempt to remedy the shortage, Bunker experimented with removing the delay pellet from Mark X BD fuzes. The results were highly successful, to his great satisfaction, and he set about altering 500 more, which were used with Battery Crockett’s 12-inch guns and Craighill’s 12-inch mortars, as well as possibly other batteries. Bunker even experimented with a 155 mm time fuze in an attempt to use a 12-inch mortar as an antiaircraft weapon! Elsewhere, he referred to the fuzes for 155 mm shells as “unreliable.”(29) In short, fuzes were a vital link in the ammunition chain. Every part of the chain — propellant, primer, projectile, explosive, and fuze — had to function properly or the defenses would fail. The Ordnance Department struggled for many years to perfect fuzes that would function effectively. Over the decades they issued successive fuzes, usually proclaiming each to be a paragon of design. Each, in turn, was succeeded by a still newer, improved design. With each succeeding improvement, fuzes became safer and more certain, yet the extreme conditions in which they were used, the conditions under which they were stored, and the conflicting requirements for safety and certainty, ensured that perfection was approached but never achieved. The element of uncertainty associated with seacoast artillery fuzes was never entirely eliminated. Sources 1.

Henry Metcalf, A Course of Instruction in Ordnance and Gunnery, (New York: John Wiley & Sons, 1891), Pg. xviii, 19.

2.

Warren Ripley, Artillery and Ammunition of the Civil War, (New York: Promontory Press, 1970), pp. 258, 273-287.

3.

John C. Tidball, Manual of Heavy Artillery Service; Prepared for the Use of the Army and Militia of the United States, (Washington, D.C.: James J. Chapman, 1880) pp. 47-51. War Department, Annual Report of the Secretary of War, Report of the Chief of Ordnance (hereafter ARCO, year), 1891, pp. 733-737.

4.

ARCO, 1891, pp. 213-237. Metcalf, pp. xviii, 6-19.

5.

ARCO, 1892, pp. 24-25, 483-486. Henry P. Merriam, “A New Percussion Fuze,” Journal of the United States Artillery (hereafter JUSA), Vol. 2, No. 1 (Jan. 1893), pp. 59-65.

6.

ARCO, 1895, pp. 499-503. War Department, Drill Regulations for Coast Artillery, United States Army, GPO, 1898, pp. 31-32.

7.

War Department, Report of the Secretary of War, Report of the Board of Ordnance and Fortification, GPO, 1896, pp. 924-25, plates 1-11.

8.

ARCO, 1900, p. 214. ARCO, 1901, pp. 16-17, 607-08.

9.

ARCO, 1902, pp. 41-42, 185-196.

10.

ARCO, 1904, pp. 34, 53-54.

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11.

Ordnance Department, Fuzes for Use in Mountain, Field, Siege, and Seacoast Powder-Charged Shell and Shrapnel and in Detonating Fuzes, Ordnance Document No. 1727, GPO, 1905.

12.

ARCO, 1905, pp. 60-61.

13.

ARCO, 1906, p. 57. Fred M. Greene, “The Fuzing of Seacoast Projectiles,” CAJ, Vol. 62, No. 3 (March 1925), pp. 231-240.

14.

RCO, 1907, pp. 67-68. Ormond M. Lissak, Ordnance and Gunnery, (New York: John Wiley, 1907), pp. 486-504. Herman W. Schull, “Fuzes and Primers,” JUSA, Vol. 27, No. 2 (March-April 1907), pp. 97-117.

15.

Ordnance Department, Fuzes for Use in Mountain, Field, Siege, and Seacoast Projectiles and in Detonating Fuzes, Ordnance Document No. 1727, GPO, 1908, tables II and IV.

16.

Wilford J. Hawkins, “Powders, Projectiles, Fuzes, and Primers,” JUSA, Vol. 38, No. 2 (Sept.-Oct. 1912), p. 165. William H. Tschappat, Textbook of Ordnance and Gunnery, (New York: John Wiley and Sons, 1917), pp. 554-555.

17.

Ordnance Document No. 1727, 1908, tables II and IV.

18.

Gunner’s Instruction, Mortar Companies, 1917-1918, (Fort Monroe, VA: Journal of the United States Artillery, 1917), pp. 25-27. W.P. Pratt, Coast Artillery Matériel, (Kansas City: Franklin Hudson Pub. Co., 1917), p. 21.

19.

Greene, “The Fuzing of Seacoast Projectiles.”

20.

McFarland, pp. 529-530. War Department, Coast Artillery Ammunition, Special Text No. 27, 1935 Edition, (The Coast Artillery School, 1938), pp. 66-69.

21.

Thomas J. Hayes, Elements of Ordnance, (New York: John Wiley and Sons, 1938), p. 593. War Department, 3-Inch Seacoast Gun Matériel, TM 9-421, GPO, 1942, p.94.

22.

War Department, 12-Inch Seacoast Matériel, TM 9-456, GPO, 1942, pp. 94, 99. War Department, 16Inch Seacoast Gun Matériel, Gun, Mk. II M1; Barbette Carriage M4, TM 9-471, GPO, 1942, pp. 276, 281. War Department, 6-Inch Seacoast Matériel: Gun M1900 Mounted on Barbette Carriage M1900, TM 9-424, GPO, 1945, p. 77. War Department, 90-mm Gun M1 and 90-mm Gun Mount T3, TM 9373, GPO, 1943, pp. 137, 143. Theodore Ohart, Elements of Ammunition, (New York: John Wiley and Sons, 1946) pp. 140-43.

23.

McFarland, pp. 517-521. War Department, Coast Artillery Ammunition, 1935, pp. 68-73.

24.

War Department, TM 9-424, pp. 78-79. War Department, TM 9- 421, p.94. War Department, TM 9373, p. 143. Ohart, p. 152-53, 170. War Department, Coast Artillery Ammunition, TM 4-205, (GPO, 1940), p. 43.

25.

War Department, 155-mm Gun Matériel, M1917, M1918 and Modifications, TM 9-345, GPO, 1942, pp. 198-199. War Department, TM 4-20, chart, change 2, GPO, 1944. TM 4-205, p. 96.

26.

ARCO, 1903, pp. 16, 46. ARCO 1904, pp. 34, 53-54.

27.

“Professional Notes,” JUSA, Vol. 40, No. 3 (Nov.-Dec. 1913), p. 383. “Professional Notes,” JUSA, Vol. 43, No. 2 (Mar.-Apr. 1915), p. 250. War Department, Coast Artillery Ammunition, 1935, p. 78. War Department, TM 9-345, pp. 201-202. War Department, TM 9-421, pp. 93-94. Seacoast Artillery, Basic Tactics and Technique, (Harrisburg, PA: Military Service Publishing Co., 1944), pp. 130-31.

28.

TM 9-373, pp. 142-43.

29.

Paul D. Bunker, Bunker’s War, (Novato, CA: Presidio Press, 1996), pp. 52, 83, 84, 88, 102.