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Alcatraz's Defenses Revamped, 1869-1876

The Plans

Board of Engineers I Report, 1868

Alcatraz, like other posts in San Francisco Bay, received no congressional appropriations for the construction of fortifications in fiscal year 1869. The reason was simple; the Corps of Engineers had not yet determined a method of constructing barbette batteries that could meet the advances of weaponry that had developed during the Civil War. But this lack of funding did not hinder the Pacific board of engineers from planning the remodeling of Alcatraz's defenses. The first breakthrough came in August 1868 when the board of engineers in New York issued a lengthy report on the question of determining the proper profile of barbette batteries. This detailed report was based on the findings of a series of experiments carried out by the board. Among the highlights of the study were several that would have considerable influence on the San Francisco engineers:

Sand was far superior to clay as the material for parapets. A parapet of sand should have a minimum thickness of 20 feet and be supported by a breast-height wall 4 feet thick. A wall within the body of a parapet was not recommended. The introduction of iron plates in parapets was generally considered inexpedient. The minimum distance between 15-Inch guns was to be 34 feet. The minimum distance between 10-inch guns was set at 22 feet. The depth of a terreplein was generally not to be less than 30 feet. A traverse was necessary for every two guns subject to direct or oblique fire and for each gun subject to enfilading fire. When practicable, a parados should be constructed for guns liable to reverse fire (Battery Mansfield). A traverse should be at least 14 feet above the terreplein, 12 feet thick at the top, and 20 feet deep to the rear. Service magazines were a necessity, the best material being well-rammed concrete.

Alcatraz's Batteries Re-designated

With these findings at hand, the Pacific board undertook the development of a plan for modifying the defenses of Alcatraz. Before discussing the plan, it is necessary to note that in May 1868 Humphreys authorized Mendell to drop the names of the Alcatraz batteries and to redesignate them with numbers. The now-familiar 8 names were replaced with 13 numbers, roughly as follows:


1--right face of Battery Halleck
2--left face of Battery Halleck
3--15-inch gun at extreme left flank of Battery Halleck and 15-Inch gun in Battery Rosecrans
4--extension of Battery Rosecrans
5--Battery Mansfield
6--northwest half of Battery Stevens
7--southeast half of Battery Stevens
8--right flank of Battery Tower
9--left flank of Battery Tower
10--right face of Battery McClellan
11--left face of Battery McClellan
12--Battery Prime
13--new battery between Prime and the wharf


The massive 15-inch calibre Rodman Cannons on Alcatraz used small cranes to hoist the solid cannonballs which could be shot at a range of 3-miles.


The Alcatraz ordinance yard situated in the court area of the Citadel.


A strong hint of the direction the Pacific board would take appeared in a letter Mendell sent to Humphreys in November 1868. Mendell had dismounted the 15-Inch gun in Battery Mansfield (no. 5) and had found the platform in such poor condition that he estimated it would cost $3,500 to rebuild it properly. He recommended to the chief of engineers that the repairs be delayed until a definite plan for a rearrangement of the defenses could be prepared: "Bearing upon this subject, I may say that the opinion is gaining strength among the members of the Board of Engineers for this Coast, that it may be advisable to cut off the top of the Island.

Proposals for Alcatraz

The Pacific board forwarded its report and plan for Alcatraz to the chief of engineers in March 1869 . It listed the objectionable features in the present arrangement of batteries on the island--such things as the high rocky slopes in the rear of the batteries and the inadequate thickness of the parapets. IIA satisfactory solution," said the Pacific board, "seems to be found only in extending the area by excavation. II In general the plan proposed leveling the southeast end of the island down to an elevation of 62 feet. This area (about one-quarter of the island) would include several batteries and future officers' quarters. The highest area would be that surrounding the defensive barracks on the former southeast peak. This would be a level plateau having an elevation of 100 feet; a large earthen parapet would surround the plateau, and a battery would face to the east over the guardhouse and the bombproof barracks. Battery 5 (Mansfield) would be excavated so that its terreplein had an elevation of 80 feet. The adjacent area, then containing noncommissioned staff "officers' quarters, would be enlarged and excavated to an elevation of 58 feet. This level space would be used for quarters, shops, and so forth.

Finally, the terrepleins of Batteries 1 through 4 (Halleck and Rosecrans) at the northwest end of the island would be greatly enlarged, but they would retain their present elevation of 48 feet. The Pacific board estimated that the total excavation would amount to 430,000 cubic yards and would cost $215,000, adding that the cost could be reduced by employing prisoners. As for armament, reported the board, "The drawing shows places for sixty-two XV inch guns, and 5 Parrott rifles in Barbette, making sixty-seven guns in barbette, and if we add the eleven guns of the casemated barracks, for which places are now ready, we have seventy-seven guns, leaving out of consideration the howitzers for the defense of the guard-room and caponnieres. This armament is regarded as ample. It may be modified by the introduction of a few XX inch guns and heavy rifles.

Humphreys passed the proposal along to the Board of Engineers for Fortifications in New York for review. In April 1869 this group returned the documents saying generally that it agreed that modifications had to be made on Alcatraz but that the costs could be reduced by requiring less excavation than that proposed. It also recommended that the new batteries in the area now occupied by Batteries Tower, McPherson, McClellan, and Prime all be moved higher up the hill. (The former rule of a maximum elevation of 48 feet did not now apply.) The New York board concluded by recommending that Humphreys direct the Pacific board to reconsider the whole subject and that it pay particular attention to- the August 1868 findings concerning traverses.

Military Prisoners Excavate

Meanwhile, Mendell made the best of his poverty and, in January 1869, asked the post commander if he could furnish prisoners for labor. The engineer was eager to begin excavating the slope in rear of Batteries 1, 2, and 3 (Halleck). At this time the Alcatraz prison contained from 90 to 125 men. General Halleck, now commanding the Military Division of the Pacific, gave his approval for a detail of from 30 to 50 prisoners, as did the chief of engineers. To encourage industry, Halleck announced that he would commute the sentences "of such as earn good reputation as laborers. " Mendell was of a mixed mind after six months' experience with these laborers: "The men are not industrious and they are careless and at times malicious in their treatment of public property but with all these drawbacks there is some profit in employing them. Whatever the quality of the prisoners' efforts, they would continue to work on engineer and quartermaster projects at all the posts in San Francisco Bay.

Defense Project Approved, 1870

Fiscal year 1870, another year without appropriations for the fortifications, would see the differences between the plans of the Pacific board and the New York board worked out and the approval of the secretary of war for a complete postwar coastal defense project for Alcatraz Island. In November 1869 the Pacific board, having considered the points raised by its eastern associates, forwarded a revised project to Washington. It accommodated New York's concepts where possible but continued to disagree on some points, particularly the elevations of the battery's terrepleins. It argued that if the batteries were placed as high on the island as the New York board thought proper, much space would be lost and fewer guns could be mounted (albeit less excavation). But the differences were not great, e.g., a reference of 100 guns for Battery5 (Mansfield) as compared to New York's 110, or a reference of70 guns for Battery 10 (McClellan) as compared to 110.

Alexander and his associates pointed out that the first batteries to be remodeled would be those at the northwest end of the island. The total excavation in this area would amount to55,000 cubic yards, "of which one fifth has already been executed during the present year at a [modest] cost of 2500 dollars, by the labor of prisoners," therefore, implying that excavation at Alcatraz would not be horrendously expensive. In the earlier plan, the officers' quarters were to be placed in an excavated area behind Batteries 10-13 at the southeast end of the island. The Pacific board retained the concept of excavating this area, but now included all quarters there, "so that the buildings shall be covered from the view of an enemy, until he shall have passed the second line of defense." (This portion of the island was eventually excavated and it served several diverse uses during the following century.)

The board of engineers in New York reviewed the new plans and in mid-December notified the chief of engineers that "we are of [the] opinion that the Pacific board have much improved their original project . . . we therefore concur, generally, in the new design for . . . Alcatraz." However, there remained changes that should be made, principally additional earthen traverses between guns. The New York board firmly believed that not more than two guns should be placed together, although it was willing to allow as many as three guns together in Batteries 9, II, and 13,"considering their slight exposure." It also recommended that separate batteries for about 25 mortars should be located on top of the island. Humphreys approved these recommendations on Christmas Eve 1869 and directed the Pacific board to make the necessary changes.

The Pacific board promptly made the desired revisions. The final plan contained forty 15-inch gun positions and no fewer than 21 earthen traverses, including both of the old capon which were to be reduced in height by having the upper gun rooms removed. The Pacific board did not think it was important to plan for mortar batteries on top of the island at this time, especially because no firm decision had yet been made concerning what would be done with the old defensive barracks there or where permanent barracks would be located. However, in response to Humphreys' directive, they tentatively placed a mortar battery on either side of the barracks: "We do not solicit approval for these particular designs, preferring to leave the question open, until the time approaches . . . construction, which may be several years in the future." The New York board now recommended approval of the project. Secretary of War William Belknap approved the project on February 19, 1870.

Estimate for New Project

The next step of this complicated procedure was for Alexander (and his associates, including Mendell) to prepare estimates for the modification of Alcatraz's works. These he forwarded to Humphreys in April 1870:

(See PDF Downloadable Version to View Chart)

Modest Beginnings

Even while recommendations were being made and approved, Mendell took steps to further the work on Alcatraz. In December 1869, he reported that he had shipped 37 excess 42-pounder rifles, 8-inch columbiads, and 8-inch and 10-inch Rodmans from the island to Benicia Arsenal. Throughout the months prisoners continued excavating at the northwest end of the island and began to demolish the gun room of the north caponier. Mendell came up with the idea of turning a 15-inch Rodman in Battery 3(Halleck) upon the caponier and knocking down the upper story with gunfire. Not only would he get rid of the masonry, he could carry out an experiment as to the resisting power of brick and concrete walls--if Humphreys approved. Humphreys did not approve:"There is no question as to the power of this gun to batter down masonry. As from the experiments at Forts Monroe and Delaware it was found that a shot striking the masonry might jarand fracture the wall for some distance from the point of impact."Such an undertaking could damage the lower-floor magazine that was to be retained in the new works.

Mendell's annual report for fiscal year 1870 showed that his work force of 45 prisoners under two civilian supervisors had made a fair start in preparation for the new works. In addition to removing the 15-Inch platform in old Battery Mansfield, they had removed the 13 columbiads in the left face of Battery Halleck (now Battery 2). They had also removed the now-obsolete shot furnace from this area. The prisoners had also completed the necessary excavations of rock in the rear of Batteries 2, 3, and 4at the northwest end of the island, "and the slopes behind the batteries have been in the main, prepared to receive the earth covering." Considerable progress had been made, too, in excavations at the southeast end of the island. As this new era of fortifications began, the War Department stated that from the beginning in 1853 down to March 1870, the appropriations for fortifications on Alcatraz Island had amounted to a total of $1,601,667.

Shortly after fiscal year 1871 began, Mendell learned that Alcatraz had received an appropriation of $50,000 for the modernization of the batteries--a sure sign that the Congress was finally satisfied that the engineers had worked out the problems of postwar defense. Mendell decided to apply most of this money towards Batteries 1 through 4 at the northwest end of the island, which together would have twelve 15-Inch platforms and seven earthen traverses, including the old caponier. He also had a crew of prisoners rebuilding the road where it passed over the top of the rear rooms of the bombproof barracks, a road that had been destroyed during the construction of the works. The reestablishment of this communication was an essential prerequisite to any major work at the southeast end of the island.