Blow out, you bugles, over the rich Dead!
There's none of these so lonely and poor of old,
But, dying, has made us rarer gifts than gold.
These laid the world away; poured out the red
The poet begins with an exclamatory command to  personified  bugles. As the reader will learn, he is demanding that they honour the sacrifice of the soldiers. The tone is militaristic; bugles, like drums, are part of the panoply of soldiering. The idea is archaic, implying timelessness; men have died in battle for centuries. 
 The “rich Dead”, with its capitalised noun, implies an abstract idea of dead soldiers representing all courageous fighters who die bravely in battle. They are spiritually “rich” because of the nobility of their sacrifice.
III. The Dead