"We surged forward like greyhounds out of the traps"

Allusion to Shakespeare’s inspiring play Henry V and the monarch’s impassioned speech before battle which starts:

Once more unto the breach, dear friends, once more

and ends:

I see you stand like greyhounds in the slips,
Straining upon the start. The game's afoot:
Follow your spirit, and upon this charge
Cry 'God for Harry, England, and Saint George!