My favorite poet for most subjects is Robert Service. He has such an abundance of poems on the subjects of war, soldiers, veterans, and "duty to country in war" (Wikipedia) that it's hard to choose the best, but these two are my favorites.
The Bard of the Yukon, on Veteran's Day.
What d’ye think, lad; what d’ye think,
As the roaring crowds go by?
As the banners flare and the brasses blare
And the great guns rend the sky?
As the women laugh like they’d all gone mad,
And the champagne glasses clink:
Oh, you’re grippin’ me hand so tightly, lad,
I’m a-wonderin’: what d’ye think?
D’ye think o’ the boys we used to know,
And how they’d have topped the fun?
Tom and Charlie, and Jack and Joe—
Gone now, every one.
How they’d have cheered as the joy-bells chime,
And they grabbed each girl for a kiss!
And now—they’re rottin’ in Flanders slime,
And they gave their lives—for this.
Or else d’ye think of the many a time
We wished we too was dead,
Up to our knees in the freezin’ grime,
With the fires of hell overhead;
When the youth and the strength of us sapped away,
And we cursed in our rage and pain?
And yet—we haven’t a word to say. . . .
We’re glad. We’d do it again.
I’m scared that they pity us. Come, old boy,
Let’s leave them their flags and their fuss.
We’d surely be hatin’ to spoil their joy
With the sight of such wrecks as us.
Let’s slip away quietly, you and me,
And we’ll talk of our chums out there:
You with your eyes that’ll never see,
Me that’s wheeled in a chair.
The March Of The Dead
The cruel war was over—oh, the triumph was so sweet!
We watched the troops returning, through our tears;
There was triumph, triumph, triumph down the scarlet glittering street,
And you scarce could hear the music for the cheers.
And you scarce could see the house-tops for the flags that flew between;
The bells were pealing madly to the sky;
And everyone was shouting for the Soldiers of the Queen,
And the glory of an age was passing by.
And then there came a shadow, swift and sudden, dark and drear;
The bells were silent, not an echo stirred.
The flags were drooping sullenly, the men forgot to cheer;
We waited, and we never spoke a word.
The sky grew darker, darker, till from out the gloomy rack
There came a voice that checked the heart with dread:
“Tear down, tear down your bunting now, and hang up sable black;
They are coming—it’s the Army of the Dead.”
They were coming, they were coming, gaunt and ghastly, sad and slow;
They were coming, all the crimson wrecks of pride;
With faces seared, and cheeks red smeared, and haunting eyes of woe,
And clotted holes the khaki couldn’t hide.
Oh, the clammy brow of anguish! the livid, foam-flecked lips!
The reeling ranks of ruin swept along!
The limb that trailed, the hand that failed, the bloody finger tips!
And oh, the dreary rhythm of their song!
“They left us on the veldt-side, but we felt we couldn’t stop
On this, our England’s crowning festal day;
We’re the men of Magersfontein, we’re the men of Spion Kop,
Colenso—we’re the men who had to pay.
We’re the men who paid the blood-price. Shall the grave be all our gain?
You owe us. Long and heavy is the score.
Then cheer us for our glory now, and cheer us for our pain,
And cheer us as ye never cheered before.”
The folks were white and stricken, and each tongue seemed weighted with lead;
Each heart was clutched in hollow hand of ice;
And every eye was staring at the horror of the dead,
The pity of the men who paid the price.
They were come, were come to mock us, in the first flush of our peace;
Through writhing lips their teeth were all agleam;
They were coming in their thousands—oh, would they never cease!
I closed my eyes, and then—it was a dream.
There was triumph, triumph, triumph down the scarlet gleaming street;
The town was mad; a man was like a boy.
A thousand flags were flaming where the sky and city meet;
A thousand bells were thundering the joy.
There was music, mirth and sunshine; but some eyes shone with regret;
And while we stun with cheers our homing braves,
O God, in Thy great mercy, let us nevermore forget
The graves they left behind, the bitter graves.