Measured mile, north targets.
To permit naval vessels to accurately gauge their speed over a short distance, three pairs of target towers were built along Herring Cove coastline, where the sea floor falls sharply off to a depth of 150 feet off Shank Painter Bar. A vessel proceeding on a course of 311 degrees 11 minutes could track its progress with reference first to the southernmost target towers, one on the shoreline, one farther upland. When the targets aligned, the vessel was at the beginning of a course extending one nautical mile (1.15 statute mile) to the alignment point of the center targets or one-and-a-half nautical miles (1.73 statute miles) to the alignment point of the northern targets. None of the towers still stand.
The brutal storms of January 2018 all but leveled dunes at the southern end of Herring Cove, opening a breach in the beachfront and revealing the long-lost footings of the outermost Measured mile, south targets. Their runic quality instantly took hold of the popular imagination. Jay Critchley transformed the three ragged concrete stubs into an environmental artwork called Shrouded Rainbow.
¶ Last updated 10 September 2018. ¶ Images from Provincetown Harbor Nautical Chart (1968), by the U.S. Coast & Geodetic Survey.
This detailed view of the 1968 nautical chart shows the three pairs of targets — six towers in all — that were used to measure a mile and a half mile.