Gunner’s Quadrant

Another stop on our vacation earlier this month was the old colonial-era Fort Matanzas.  With all due respect to Mannie, I think the rangers there have the best posting in the National Park system, what with the beach and getting to ride the shuttle boat all day.  While the fort dates to Spanish times and saw no Civil War activity that I am aware of, the site is worth a visit if you are in the St. Augustine area.

One display that caught my attention, which put me on a Civil War tangent (nice word play don’t you think?) was this device:

Ft Matanzas 1 Aug 11 314

It is a reproduction gunner’s quadrant hanging from a reproduction Spanish gun.  These devices have been around practically since the first artillery pieces. Woodcuts depict the use of such with ancient guns.

Rather simple application of geometry and physics.  The quadrant provides a rule by which to measure the elevation of the gun using a plumb line.  Of course all the gunner had to do was figure the range to target, prescribe the powder load, account for wind and environmental factors, factor gun placement, and then calculate the desired elevation.  Sure!  No problem there so long as I remember how to use long hand mathematics while consulting those sine-cosine-tangent tables in the back of the book!

Yes, line-of-sight systems are easier to employ.  That’s why by the time of the Civil War most field artillery came with breech and muzzle (or trunnion) sights.  Be these tangent, pendulum,  or simple fixed sights, the gunner would elevate the cannon based on alignments along the bore.  But the gunners held on to the old quadrant for some contingencies (much like they retained the old match cord for emergencies even after friction primers were perfected).  Larger guns, particularly mortars, still required the use of quadrants.  Take a look at the lower left in this photo of the “Dictator.”

One of the items in the basket on the railcar is a quadrant.

While the quadrant might seem ancient, the tool is still on the gunner’s kit today.  During World War I, the Army fielded a quadrant which used a leveling bubble instead of the plumb line.  That device, with refinements, continued in use as the “Quadrant, Gunner’s, M1” well into the 21st century.  Even the advanced M109 self-propelled howitzers with their completely computerized firing systems, calculating everything from ambient air temperature to the droop of the gun tube, retain the option to “go manual” using the old gunner’s quadrant.

Note "seat" for quadrant on top of sight

Although I would say in my time around the gunners, they loathed using the old “iron sights” – too much math involved!

6 thoughts on “Gunner’s Quadrant

  1. When I was an Artillery Marine in the late 80’s, the Section Chief used the gunners quadrant before every round was shot down range.

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