Here are some well-known words and expressions found nearly in every language. All of them owe their meaning to some military fact, incident, event, object, person, etc.
Trojan Horse. The myth has it that during the Trojan War the Greeks besieging Troy without success resorted to a ruse. They built a huge wooden horse and left it standing near the walls of the fortress of Troy, and themselves made a demonstration of sailing away. The Troy inhabitants dragged the horse into the city. At night the warriors hidden in the horse jumped out and, killing all the guard, opened the gates of the fortress and let in their comrades who had returned by ship. In this way Troy was seized. Hence, the figurative meaning "cunning plan'.
The sword of Damocles. Now the expression is used to mean always present deadly danger. In mythology Damocles has a sword hanging over his head on a thin thread (or hair) as a reminder of constant menace to his life.
With the shield or on the shield. It means to be the victor or die with glory. In ancient Greece warriors triumphantly returned from a war with their shields while the dead were carried from the battlefield on the shield as a form of honoring them.
The old guard never surrenders; it only dies. Napoleon's elite troops which were surrounded with a halo of invincibility were called 'old guard'.
General's battle. Fighting in which the main thing is the skillful leadership of commanders. The opposite meaning has the phrase 'soldier's battle' in which the issue will mainly depend on the soldier's brave and competent action.
At the point of the bayonet. By force of arms.
Let loose (unleash) the bloodhounds of war. An expression meaning figuratively 'trigger off a war'.
Be quick on the draw. Act quickly. Allusion is at drawing a blank weapon (sword or dagger) from the sheath quicker than the enemy. In America the phrase was popularized by stories from Wild West about cowboys quick in drawing their pistols whereever they were and being the first to fire.
Every soldier carries the marshal's baton in his knapsack. Napoleon considered every soldier a potential leader, and wanted his officers to encourage this. That way, when a Lieutenant was killed, the men would continue to fight. Napoleon always considered his privates and corperals to be future captains and generals.
Every soldier carries the marshal's baton in his knapsack. Napoleon's expression, meaning figuratively 'he is a bad soldier who doesn't dream of becoming a general'.
Panicky fear. In the Greek mythology Pan was God of woods and shepherds who inspired with terror even troops who were thrown into a headlong flight at his appearance.
Hammer swords into ploughshares. A phrase from the bible from a prophecy by an apostle predicting times to come when peace will reign supreme in the world.