Jan Fischer, American Soldier In His Military Life

Arguably the greatest invention that affected not just the military, but all society, after adoption of fire, was the wheel, and its use in the construction of the chariot. There were no advances in military technology until, from the mechanical arm action of a slinger, the Greeks, Egyptians, Romans, Persians, Chinese, etc. development the siege engines. The bow was manufactured in increasingly larger and more powerful versions to increase both the weapon range and armour penetration performance. These developed into the powerful composite and/or recurve bows, and crossbows of Ancient China. These proved particularly useful during the rise of cavalry, encased in ever-more sophisticated armour, dominating the battlefield.
Somewhat earlier in medieval China, gunpowder had been invented, and was increasingly used by the military in combat. The use of gunpowder in the early vase-like mortars in Europe, and advanced versions of the long bow and cross bow, which all had armour-piercing arrowheads, that put an end to the dominance of the armoured knight. After the long bow, which required great skill and strength to use, the next most significant technological advance was the musket, which could be used effectively with little training. In time the successors to muskets and cannon, in the form of rifles and artillery, would become core battlefield technology.
As the speed of technological advances accelerated in civilian applications, so too warfare became more industralised. The newly invented machine gun and repeating rifle redefined fire power on the battlefield and, in part, explains the high casualty rates of the American Civil War. The next breakthrough was the conversion of artillery parks from the muzzle loading guns to the breech loading guns, and in particular the highly mobile, recoilless, field-gun, the French Soixante-Quinze, in the late 19th century.
The development of breech loading had the greatest effect on naval warfare, for the first time since the Middle Ages altering the way weapons are mounted on warships, and therefore naval tactics, now divorced from the reliance on sails with the invention of the internal combustion. A further advance in military naval technology was the design of the submarine and its weapon, the torpedo.