Armies march on their stomachs. Historically, this often meant that armies marched with their bakeries. Military field manuals are a source of information in simple impromptu oven construction. The simplest oven is the item 496: An oven may be excavated in a clay bank (Fig. 6) and used at once. Few of us have sloped clay banks in our yards that can be dug into for an oven, but this suggests the possibility of ovens as a technical possibility long before there were even mud earth structures. But a more practical oven is the first of the two ovens described in item 495. It is an oven built by slathering clay over a barrel. This is so similar to the Sunset Magazine’s oven built over a cardboard trash barrel that I would not be surprised if a military oven were not the inspiration for Sunset’s instructions.

For the second oven a very simple hearth — a “pit” dug 6 – 12 inches deep is all this specified. I’d think that that pit was probably filled with clay to form the oven floor, but I am only speculating.

495. —To bake bread, when none of the portable ovens of the Commissary Department are carried, improvised ovens must be constructed. The simplest method is to take a barrel with one head out (one with iron hoops best), lay it on its side in a hollow in the ground and then plaster over with wet clay 6 to 8 in. thick, then with a layer of dry earth equally thick, leaving an opening of 3 or 4 in. at the top of the closed end for a flue. The staves are then burned out by a hot fire, which also bakes the clay covering, forming an arched oven. To bake, after beating, the front and flues are closed. Or a pit may be dug from 6 to 12 in. deep and 4 by 5 ft. for the hearth, over this form an arch with a hurdle or any other material available (Fig. 7). with a chimney at one end and a door at the other. Then plaster and cover the arch as in the barrel oven and bake the clay covering.

496. —An oven may be excavated in a clay bank (Fig. 6) and used at once.

Manual of military field engineering for the use of officers and troops of the line
By William Dorrance Beach, Edwin Alvin Root, Thomas Horace Slavens, United States Infantry and Cavalry School. Dept. of Engineering, Kansas City, Mo. : Hudson-Kimberly Pub. Co. ; London [England] : W.H. Allen & Co. 1897.