Machineguns which changed the assault tactics during WWI, although they were invented before. Begun the trench and static war.

Originally Posted by LeEnfield

Steam Turbines

Steam turbines for ships invented in 1890s in England. Seems he had a ship built(Turbinia) that ran riot through the Naval Review for Victoria's Diamond(?) Anniversary. WWI trench warfare preceded @ Petersburg, Va during Civil War. Also armored trains, land mines.

Bailey Bridge, WWII

Computers WW2

Originally Posted by Padre

Probably the first example of balloons being used in warfare date to 2-3rd Century China (Kongming Lantern) and invented by Zhuge Liang.

Probably wasn't invented by Zhuge Liang.
In the East, in most cases, the actual inventor is never credited, rather the top boss is. Also there is evidence that experiments with signal balloons like the Kongming Lantern date back before Zhuge Liang.
Normally I'd be skeptical about the "it dates before" claims but I think in this case it's pretty consistent with how things are done in this part of the world.

Ambulances

Ambulances were first used for emergency transport in 1487 by the Spanish, and civilian variants were put into operation in 1887.

During the American Civil War vehicles for conveying the wounded off the field of battle were called ambulance wagons. Field hospitals were still called ambulances during the Franco-Prussian War of 1870 and in the Serbo-Turkish war of 1876[7] even though the wagons were first referred to as ambulances about 1854 during the Crimean War.

i don't know that it belongs to any single war, but the search for a smokeless gunpowder brought chemistry and its techniques firmly into the mainstream of industrial development.
similarly the search for a single cast cannon does not belong to any one war but it changed our understanding of the nature of metals and, through this, the world.

I've thought of parachutes, but it seems more like a civilian development that was quickly adopted by the military than vice versa.

Field Rations (Combat Rations).
Used to feed soldiers on the move, now used in a variety of ways for anyone who may not be near a kitchen for a while.
I would really like to know who first invented them!

The airplane, first flown by the Wright Brothers in 1903, perfected and publicized as a means of transporting people and goods after World War I (1914-1918)

Originally Posted by bigcanada813

The airplane, first flown by the Wright Brothers in 1903, perfected and publicized as a means of transporting people and goods after World War I (1914-1918)

Not exactly a military invention though... that's what's nagging me about some of the inventions I was thinking of. Like the parachute.