coast defense

Masthead Image

Boston Harbor Defenses: Overview and History

In 1797, Boston Harbor had only one defensive position: Ft. Independence--a wooden fort on Castle Island--that faced eastward over the western (main) channel into the port. Then in 1808, a second fort, initially named Ft. Warren, was built about one mile farther north, on Governors Island, to control the eastern channel into Boston. [Today, Castle Island is no longer an island, and Governors Island was leveled in the building of Logan Airport. According to FortWiki, the southern end of Logan's runway 4R is roughly the site of the old Governors Island fort.] Slide 1 at left shows a map that labels in pink the locations of these two earliest forts in Boston Harbor (plus a third--Ft. Warren). Slide 2 at left gives a good idea of how Castle Island and Governors Island loomed over the west and east approaches to the harbor.

This bird's-eye view of Boston Harbor dates from 1870 and shows the two original island forts (in the mid-distance) still guarding the channel. The image shows a 4th of July celebration, with both forts (plus Ft. Waren, in the distance) firing salutes. Clicking on this image will zoom it for closer inspection.

Although the guns of these two forts could fire barely half a mile with accuracy, the fire of attacking ships of the period was of even shorter range. Back then, most naval engagements were fought at ranges below 300 yards, and ships' guns could not elevate sufficiently to fire at forts sited on heights. Consequently, the British, who frequently menaced Boston by land during those early days, never attempted to penetrate Boston's harbor defenses, and no Boston seacoast gun ever had to fire a shot in anger. This history of successful deterrence was unchanged for over 150 years. What did change, and with increasing rapidity, were the numbers and locations of the harbor defenses, the types and sizes of their guns, and the array of technologies brought to bear on the tasks of coast defense.

[The reader might want to pause here to consider in detail the geography of Boston Harbor, its islands and its channels, using this 1901 map. This map is maintained on-line by the Boston Public Library, is interactive, and can be zoomed to several levels. Slide 1 is a select portion of this map.]

Ft. Independence was rebuilt between 1834 and 1851 (see Slide 3). Ft. Winthrop was rebuilt as a stone fort with outlying works between 1808 and 1833 (see Slide 4), and the new Ft. Warren was built on Georges Island between 1833 and 1861.

By the 1890s, however, America had begun to worry that its smooth-bore cannon forts were not strong enough to deter the battleship fleets of "rogue" South American republics, much less the British Navy, which it was feared could sail into our harbors and demand tribute, shell our cities, or land troops on our shores almost at will. These fears gave birth to the Endicott Board, which in its 1886 Report drew up recommendations for a vast expansion and technological upgrade of U.S. coast defenses. A budget of $100 million (the equivalent of $2.4 billion in 2010 dollars) was requested by President Grover Cleveland to build new forts and re-arm older ones in 29 named harbors across the country. The Endicott Board named Boston as #3 on its priority list of ports (after New York and San Francisco), and requested a total of 43 big guns and 132 coast defense mortars for the city.

The Endicott Report triggered a vast, nation-wide fort-building program that included construction of the concrete forts familiar to Bostonians today. A Google Map locating these forts is shown in Slide 5. In the pre-WW2 era, a total of nine new concrete forts, scattered around the Harbor Islands and in Winthrop and Nahant, joined Ft. Warren, which itself received several new gun batteries. The pre-WW2 forts are also shown in Slide 1, labeled in blue. Since naval guns had now become much more powerful, the new forts had to be constructed farther out from Boston proper to prevent enemy ships from standing offshore and shelling the city. Boston's typical "big guns" of the pre-WW2 period were the 12-inch DC (disappearing carriage) guns at Forts Heath, Warren, and Revere. These had ranges of between 6 and 8 miles, depending on their vintage. The 12-inch mortars could drop their shells on the enemy at ranges in excess of 7 miles. Then there were the 12-inch guns of Ft. Ruckman in Nahant and the 16-inch weapons of Ft. Duvall in Hull. These guns, installed in the 1920s on open barbette carriages capable of higher elevations, could reach out 15 and 28 miles respectively.

The Endicott Board's program also included the construction of facilities to maintain and control groups of submarine mines that would be planted across the main channels into Boston Harbor if and when hostilities threatened. A number of searchlights, used to direct the guns, were added to the harbor forts in the 'teens and twenties.

Just prior to WW2, a "Modernization Program" was set forth for all U.S. harbor defenses, including Boston's. Some additional gun positions, built at "military reservations" instead of forts, were placed on East Point in Nahant, Outer Brewster Island, and Fourth Cliff (south of Scituate). New 16-inch guns were emplaced at East Point, and new rapid-firing 6-inch batteries were built at East Point, Outer Brewster, and Fourth Cliff. In Slide 1, the facilities labeled in red on show the scope of the harbor defenses during WW2. Slide 6 identifies the WW2-era Location numbers of facilities in the inner harbor. As the war came on, the 10-inch and 12-inch guns on disappearing carriages and the 12-inch mortars, all of which had been introduced to the harbor forts over the past 35 years and had previously been Boston's "big guns," were declared obselete and steadily abandoned.

As longer-range guns were introduced, the chain of fire control towers that ran along the coast and was used to find the positions of enemy ships was greatly expanded prior to WW2. Slide 7 shows the extent of these new structures. A fire control radar was added for each of the major WW2 gun batteries, and positions for anti-aircraft observers were added to the tops of many of the fire control structures.

Boston Harbor Maps, Charts, and Images

  • The History of Boston's Harbor Defenses
    This map, dated 1873 but based upon data from earlier in the 1800s, is a segment of a larger map by Nathaniel S. Dearborn in the Leventhal Map Center at the Boston Public Library, and can be viewed on-line. It has been sharpened and annotated by The three forts in pink were built prior to the Civil War. Those in blue were built in the pre-WW2 period, from 1890 to 1935. The two sites shown only in red were built just before and during WW2. All pre-WW2 forts were also active during WW2, and so are shown with both blue and red captions. Ft. Warren, was built before the Ciivil War but was active in the pre-WW2 period and also during WW2. The four facilities with arrows at the top of the map were located in Winthrop or Nahant, just beyond the northern edge of this map. An approximate scale is at lower left, and the soundings shown are in fathoms, at low tide. Shaded areas in the harbor are mud flats at low tide.
  • Castle-William-1777
    This sketch shows Castle William (later Ft. Independence) on the left and Governor's Island (later the site of Ft. Warren, re-named Ft. Winthrop) on the right. It looks northerly towards the center of Boston. The image is from the Leventhal Center at the Boston Public Library, and has Call No. G1106.P5 1781 .D4.
  • Fort Independence 1852-S
    This image, from Wikipedia Commons, looks easterly at Fort Independence on Castle Island. Governor's Island, with the original Ft. Warren atop it, is across the channel, in the background.
  • Governor's Island 1865
  • Inner Harbor Forts
    This map provides a closer view of the forts and islands of the inner harbor defenses during WW2. The numbers in parentheses are the "Location" numbers assigned by the Army during the war. Ft. Banks (at top) was the site of the central command for all the harbor defenses (Harbor Defense Command Post-HDCP). Ft. Dawes was the site of the Harbor Entrance Control Post (HECP), a cooperative Army-Navy observation station (with an area-wide radar) that controlled all harbor traffic during the war. Hog Island (lower right), the site of Ft. Duvall, has since been renamed Spinnaker Island by the developers who covered it with condos.
  • Boston Harbor Forts-labeled
    This map identifies the forts and major sites in the Boston Harbor defenses. Up through WW2, the northern-most gun position, East Point, was not a named fort, nor was the southern-most, Fourth Cliff (not shown here). But from the outset, almost all the gun positions were located within the harbor mouth formed by East Point (Nahant) on the north and Pt. Allerton (Hull) on the south. Fort Independence, in South Boston, just across the channel from Logan Airport, was built in the late 1700s and is shown here to show how the increased power of guns has influenced the location of harbor defenses over the past 150 years.
  • Boston Harbor Overview-labeled
    This map summarizes the extent of Boston's hHarbor defenses in WW2. Castle Hill was the site of the northern-most fire control tower of that era, and Gurnet Point was the southern-most. Straight-line distance between these two fire control structures is about 55 mi. Other selected fire control tower sites are named on the map. The two heaviest gun batteries in WW2, the 16-inch guns of East Point and Ft. Duvall are also labeled. These guns could cover the entire coastal area shown on this map. Battery Murphy at East Point was the northern-most in the Boston harbor defenses, and Battery 206 at Fourth Cliff was the southern-most. Defense to the north was also aided by the 16-inch guns of Battery Seaman in Portsmouth, NH, which could fire down to just past Halibut Pt.