Edwards Ferry – More Notes on the “Numbers”

One good thing about the blogging format, at least the way I’m using it here, you get to see my research on this subject as it evolves.   The down side of course, YOU get to see my research on this subject as it evolves, warts and all!  Such is the case here today, as I was reviewing some old notes.

I’d completely forgotten about a study in 1963 by Colonel A.B. Johnson.  Johnson explored the logistical issues for the passage of the Army of the Potomac through Loudoun County.  His study on the topic was far, far more exhausting than mine, and focused more on the length of supply trains needed to keep the army moving.

Simply put, Johnson calculated many more of the variables, for instance the break in the line of march between units and the interspersing of officers horses.  He also tabulated the raw number of horses in the column – 15,000 for the cavalry, 6,100 for the artillery, and 1,948 of the officers of the infantry – totaling 35,048.  And another bit for those interested in the logistical numbers, he calculated, based on a factor of thirty supply wagons for every thousand men, that 3,000 wagons supported the Army of the Potomac.

Get the calculators out.  Johnson estimated for 77,000 infantry (a number higher than the actual returns in the Official Records), counting officer’s rides and breaks for the units, that column of fours along was 23 miles long.  The Cavalry column was 8.5 miles.  And the artillery covered 10 miles.  Those 3,000 wagons presented another 35 miles of traffic.

My “straw man” numbers were based on the “engineered throughput” of the bridge.  Johnson’s are more practical for staff planning.  So let me compare those:

Engineered Throughput Johnson’s “Staff Planning Throughput” Actual
Length of Combat Arms Column: 26 miles 41 miles Note 1
Length of Trains: 22 miles (Note 2) 35 miles Note 1
Total Column: 48 miles 76 miles (83.5 miles?) (Note 3) 195 miles (Note 4)
Time to Pass at 3 mph: 16 hours 25 to 28 hours 65 hours
  • Note 1:  Separating the actual length of the combat arms and supply trains is next to impossible, as the Corps crossed with their trains.
  • Note 2:  I’ll accept Johnson’s estimates on the supply train numbers but reference the engineer’s 40 feet planning length of a wagon, vice Johnson’s 60 feet.
  • Note 3:  Johnson arrives at a number of 83.5 miles, but his numbers add up to 76 miles.  I’ll offer both figures here.
  • Note 4:  This is a swag on my part – 65 hours at 3 mph produces 195 miles.

Thus, the “perfectly harmonious crossing” which is only governed by the bridge’s engineered capacity would take 16 hours.  The “perfectly ordered” crossing based on a staff assessment of the numbers would take around 28 hours.  The reality was 65 hours.

Johnson’s numbers relate another important factor to consider.  Take the higher number of 83.5 miles.  Imagine the crossing made today, using US 15 between and the modern bridge at Point of Rocks, Maryland.  On that route, Gettysburg is roughly 60 miles north of Leesburg.  Thus as the lead elements of the Army of the Potomac reached Cemetery Hill, the end of the column would still be 23 or more miles SOUTH of Leesburg!

At any rate, you have my “straw man” of 16 hours to pass through Edwards Ferry, in a theoretical world with all the traffic lined up like well disciplined geese.  A more practical assessment was a 28 hours, if all the formations were behaving smartly.  Then the reality of 65 hours.

Engineered Throughput Johnson’s “Staff Planning Throughput” Actual
Length of Combat Arms Column 26 miles 41 miles Note 1
Length of Trains 35 miles (Note 2) 35 miles Note 1
Total Column 61 miles 76 miles (83.5 miles?) 195 miles (Note 3)
Time to Pass at 3 mph 20 hours 25 to 28 hours 65 hours

Published by Craig Swain

"Historical marker hunter" and Civil War enthusiast.

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