Seems it was written about a military initiative in spring 1917 but was there a name for the battle itself? I can't seem to find a reference anywhere...
Owen does not label a particular action in the poem, but there is supporting evidence to suggest it was inspired by a specific event. Shortly before writing the poem, he put this in a letter home on the 25th April:
Immediately after I sent my last letter…..we were rushed up into the line. Twice in one day we went over the top, gaining both our objectives. Our "A" Company led the attack and of course lost a certain number of men. I had some extraordinary escapes from shells and bullets.
Digging through the history of Owen's Battalion, the 2nd Manchesters, reveals that the likely action took place on the 14th of April. The troops were ordered into an attack on a trench complex on the western side of St. Quentin in northern France.
To reach the jump-off point, the soldiers took a long march during which they rested in the shade of a hill.
Halted against the shade of a last hill,
They fed, and, lying easy, were at ease
After resting, they plunged into the assault over a ridge on the hill and were shelled by German artillery, suffering casualties.
To face the stark, blank sky beyond the ridge,
So, soon they topped the hill, and raced together
Over an open stretch of herb and heather
Exposed. And instantly the whole sky burned
With fury against them; and soft sudden cups
Opened in thousands for their blood; and the green slopes
Chasmed and steepened sheer to infinite space.
On reaching their final objective, they found the German trench empty. After the action, most of the battalion was sent back to their HQ at Savy Wood to rest.
And crawling slowly back, have by degrees
Regained cool peaceful air in wonder—
Why speak they not of comrades that went under?
This is not definitive evidence, but given the strong circumstantial links in the dates and description of events, it seems likely this is the action which inspired the poem.
Source: ST QUENTIN 1914-1918 - Hindenburg Line by Helen McPhail and Philip Guest