How is irony used to increase the impact of the poem "War is Kind"?

"War is Kind," by Stephen Crane, is an ironic poem about
the horrors of war.

The poem contains a number of gruesome
images of war. Some of them are:

a) "your lover threw wild
hands toward the sky

And the affrighted steed ran on
alone"

b) "A field where a thousand corpses
lie";

c) "your father tumbled in the
yellow

trenches,

Raged at his
breast, gulped and died."

The poem also includes some
disparaging comments about soldiers: the poet refers to the soldiers as "men who were
born to drill and die," and as "little souls who thirst for
fight."

Interspersed amongst these realistic and gruesome
images and comments is an ironic refrain: "Do not weep, War is kind."  This is a classic
and forceful use of irony, which is when an author says one thing and means the exact
opposite.