Major Roy commanded C Squadron of the 20 Lancers in the 1965 war. The squadron was in charge of anti-infiltration operations and in mid- August at a position west of the river Munawar Tavi. On September 1, Pakistan shelled area heavily and followed by a tank thrust, crossing international borders.
To stem the advance , Major Roy deployed his armour and men skillfully . In their first encounter, his squadron destroyed 6 enemy tanks and captured a jeep. When Pakistan launched a second attack, a fierce battle ensued for the next few hours.. But the Pakistani Patton tanks were beaten back decisively.13 of them were destroyed and many others irreparably damaged, The Pakistani offensive was thus effectively pushed back and their attempts to encircle the infantry Brigade group thrawted.
For his skill and expert marshalling of resources, Major Roy was awarded the Mahavir Chakra in 1965.