2015.0017 Calipers, view 1
  • 2015.0017 Calipers, view 1
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Tool (for firearm) (Calipers)

  • Category:


  • Creator (Role):

    Frankford Arsenal (Manufacturer)

  • Place of Origin:

    Philadelphia, Philadelphia, Pennsylvania, Mid-Atlantic, United States, North America

  • Date:


  • Materials:

    Brass; Iron

  • Techniques:


  • Museum Object Number:


  • Complete Details

Object Number


Object Name

Tool (for firearm) (Calipers)



Credit Line/Donor

Museum purchase with funds provided by Mr. and Mrs. Frank L. Hohmann III

Creator (Role)

Frankford Arsenal (Manufacturer)

Place of Origin

Philadelphia, Philadelphia, Pennsylvania, Mid-Atlantic, United States, North America

Origin Notes

Made just north of Philadelphia in the township of Frankford, PA.



Mark or Signature or Inscription or Label

1. Mark; Bow, inner curve; "LIEU\T. M. THOMAS U.S. ORDNANCE" "FRANKFORD. PA. 1819" stamped incuse
2. Inscription; Bow, inner curve, near hinge; "Franklin Buchanan" in script


Military; Nautical; Science; Civil War; War of 1812


Brass; Iron



Dimensions (inches)

7 (L)

Dimensions (centimeters)

17.78 (L)

Measurement Notes

Measurement when closed.

Object Description

Web - 07/01/2015

This is a deceptively simple brass instrument used for the complex predictions of a gunner’s success in range of fire. The steel tips could measure a gun’s (cannon’s) bore, and a shot’s diameter combined with its weight, to calculate the powder rating and thus the gun’s range using the engraved mathematical scales. This artillery instrument’s design was developed as a “caliber rule” or “gunner’s caliper” by the mid-1600s and used on the Continent, Great Britain, and the Americas well into 1800s. It served as part of the complement of instruments devised to calculate efficacy of artillery on land and sea. This particular pair of calipers is marked for the U.S. Arsenal established in 1816 in Frankford, Pennsylvania (now a suburb of Philadelphia). The 20-acre arsenal produced ammunition, artillery instruments and gauges for American military use. One of the calipers' inner bow edges is stamped incuse with the name Lieut. M. Thomas and the date 1819. Tthe name of a second owner is engraved on the opposite bow near the pivot hinge: “Franklin Buchanan.” Presumably these government-issue calipers transferred to U.S Naval officer Franklin Buchanan (1800-1874) early in his notable career trajectory from 15-year old midshipman to officer, to lieutenant, to commander, to captain and first superintendent of the Annapolis Naval Academy (1845), to commander on Perry’s mission to Japan, and ultimately to his dismissal in 1861. Buchanan and his wife Ann Lloyd Buchanan lived on their family property in the Eastern shore of Maryland. Thus in 1861 when war commenced, he enlisted in the Confederate Navy and served as a commander until imprisoned. His fame today is for serving as first captain (flag officer) of the iron-clad C.S.S. Virginia (“Merrimack”). While it is possible that Buchanan possessed these calipers during the Civil War, it is not probable that he used them much after his time at the U.S. Naval Academy, nor later as a fleet commander.