Dírnaith was a wedge-shaped battle formation invented by the Númenóreans and mostly used by the Dúnedain of Middle-earth. The technique was designed to work over a short distance and cleave through the enemies' ranks and scatter them into disarray. If Isildur had been in a better position when ambushed by the orcs at the Gladden Fields, he would have commanded his men to form a Dírnaith and the battle might have gone differently.