Very helpful book, covers foot anatomy, biomechanics, treatment of injuries, and shoe maintenance and construction with lots of diagrams and X-rays:
The Soldier's Foot and the Military Shoe
Munson's requirements for a shoe:
a) A good military foot covering should be well joined, strong, substantial and solid, yet at the same time sufficiently flexible to permit of the natural functioning of the joints. It must be supple, so as to avoid the undue loss of necessary energy in overcoming resistance of the leather with each step likewise to reduce the liability to blister and other injury.
b) The shoe must be comfortable.
c) The shoe must be durable. ... The main wear of course falls on the soles.
d) The shoe should be as simple and neat as possible.
e) The foot covering should be as light in weight as is compatible with serviceability.
f) The shoe must be made in such a way that the soldier can easily put it on and take it off.
g) The material of which the shoe is made, and the special treatment of the former, must be such as will facilitate evaporation of moisture from within, yet not to a degree by which the absorption of moisture from without is unduly favored.
h) The material or leather of the shoe upper must not be hard; otherwise it will cause blisters, callouses and corns.
i) The cost of the military shoe is a consideration quite secondary to the one of efficiency.
j) ...a sufficient number of sizes as to length, and letters as to width, must be provided in order that the foot of every soldier may find a shoe of dimensions to properly cover it.
k) The shoe should be perfectly smooth in the interior, especially the insole, the part surrounding the heel and the uppers over the fore foot.
l) The heel should be broad, flat, long and solid. ...the outer half of the heel is heavily reinforced with iron nails. The heel must be low ... Finally, the plane of the lower face of the heel should correspond with that of the sole, so as to give the most secure bearing surface on standing.
m) The inside of the shoe over the heel should not be too wide.
n) The posterior wall of the shoe should be curved so as to embrace the natural curvature of the heel.
o) The shoe should not support the arch of the foot in the sense of lifting it up or buttressing it from below.
p) The sole should be sufficiently thick to prevent the foot from being injured by inequality in the ground.
q) The sole should be flat across, to furnish a level surface for the foot and a more secure hold upon the ground in steadying the body in standing and marching. ... It should have a slight upward curve at its forward end to prevent the toe catching in unevenly raised places on the walking surface, and to permit of accomplishing the heel-and-toe-walking of the marching step.
r) There must be plenty of room across the ball of the foot, so that there shall be no constriction of the weight bearing foot at that point.
s) The toe cap must be high, so as to avoid any hurtful pressure on the toes below. It must also rise abruptly from the front of the shoe, without forming an acute angle into which the front of the toes may be wedged in walking.
t) The material of the quarters must be pliable.
u) There should be no stiff or excessive leather, or rows of stitching, so located as to be immediately over any of the extensor tendons of the toes, which lie close to the surface over the instep. This particularly applies to the extensor tendon of the great toe.
v) The tongue should be as small as possible to prevent bunching and wrinkling under the laces, with injury to the instep.
w) The front of the quarters must be sufficiently cut away so that the rows of eyelets may be well separated in order to provide elasticity in the fitting of different heights of instep.
x) Eyelets, and not hooks, must be used for the laces.
y) The shoe must have such a shape that it will not contain any useless dead space, since these require extra material as a covering, which would cause unnecessary weight and encumbrance to the foot.
z) The shoe must also have such a shape as to permit of the great toe returning toward its proper alignment to the degree which the average age and ordinary foot deformity of the soldier class would warrant reasonable expectation.
Neat trick: pack wet leather shoes with dried oats to dry them overnight. The oats swell and prevent the leather deforming while drying out.