As our attention turns to Fredericksburg, the topic of pontoon bridges enters the sesquicentennial threads. I’ve discussed the nature of constructing these bridges in detail, with respect to those placed at Edwards Ferry in June 1863. We think of the wooden pontoons most often within the context of the Civil War. Big wooden boats like the ones on display at Chatham overlooking Fredericksburg today.
These were not the only type of boats used for pontoon bridging during the Civil War. One alternative was a frame, either wood or iron, with either canvas or rubber covering. An example of the frame with canvas type appears in a wartime photo taken at Rappanannock Station in 1864.
Almost looks like it was setup on some display just for the benefit of the photographer!
The canvas boat was of course lighter and easily broken down for transport. But there were some down sides to canvas boats. A message from Major (or was it Brigadier?) General Horatio Wright to Major General William Rosecrans in early December 1862.
I’m pulling this message out of context, so some background is in order. Considering his orders and line of march, Rosecrans decided the Army of the Cumberland, or Fourteenth Corps if you prefer, needed a pontoon bridge set. He figured on about 700 feet of bridging. Authorities in Washington approved, and directed Rosecrans to order the equipment from Cincinnati, where engineers in General Wright’s Department of the Ohio could supervise the outfitting. There was some back and forth about the type of boat to issue – wood or canvas. The preference of the Army’s engineers is apparent in Wright’s response on December 7, 1862:
Canvas boats are not so reliable as wooden ones. Unless great care is used, canvas necessarily mildews and then soon rots. If used by soldiers for shelter, it would soon become damaged for boats. It is not entirely water-proof, even after it lies in the water some time. It is doubtful whether canvas boats are as reliable in ordinarily rapid streams as wooden ones, especially if the bridge’s required to serve a long time, as on a line of communication. Canvas is more easily punctured and worn by floating bodies, and requires to be taken out of the bridge to be well repaired. It takes more time to unload, put together, and launch a canvas boat than to simply unload and launch a wooden one. According to Duane’s book, a canvas boat train requires as many wagons to transport it as a wooden one. Wooden boats can be produced here as rapidly as canvas ones, and are rapidly calked and repaired when leaky, provided they are made of seasoned timber. Wooden boats are much better for use as boats, or to combine into rafts. Unless for a very short campaign, with careful and experienced engineer troops, I would advise the adoption of wooden boats. Buell’s pontoons were made of green lumber. We can get seasoned now. Shall I order wood or canvas?
The reference of “Duane’s book” is, I believe, to the Manual for Engineer Troops by Captain James C. Duane. As an instructor on various engineering topics, Duane had the opportunity to research pontoon bridging, compare to practices in other armies, and experiment with different materials.
I could probably pull another dozen pages from the manuals and wartime accounts to further illustrate respective advantages and disadvantages of wooden boats vs. canvas frame boats for pontoons. Wood, at least seasoned wood, was more durable and required less maintenance. Not mentioned, but cited in the engineering manuals of the day, wood stood up well against rocky stream bottoms, where canvas ripped.
With respect to the number of wagons needed, there’s a lot of other factors that were not considered with Wright’s response. Duane indicated a wooden boat, or “French style,” pontoon train required 34 wagons each loaded with a pontoon boat, seven balks, numerous lashings, oars, boat-hooks, and an anchor. On the other hand the canvas train required 29 wagons each with a canvas pontoon, trestle, with balks, oars, and boat-hooks. Notice the canvas boat wagons included some, if not all, the superstructure of the bridge. The wooden pontoons, being fixed size and structure, were much more bulky on the road. The wagon carrying the canvas pontoon was smaller and lighter.
Wartime experience called upon some reassessment in regards to the preference of materials. In 1869, a board of engineers submitted a new manual covering bridging operations (eventually approved and published in 1870). The board noted:
With regard to the canvas boat, it soon became apparent that it was precisely what we required for our advance-guard train. It is light, simple, strong, easily repaired, and when packed can safely be transported with the superstructure of the bridge as rapidly as any column of troops can move.
The board of officers submitting this manual included Duane. The board also noted that the canvas bridging also worked well for expedient ferry operations.
I’ve found no direct record to confirm the type of pontoons delivered to Rosecrans. The Army of the Cumberland used both types at times later in the war, for what it is worth.
But turning back to the Eastern Theater for a moment – what if Major General Burnside’s pontoon train had included a set of these “advance guard” canvas pontoon boats?