Was the armor thin enough back then that it could knock a tank out, or only disable it? Once enemy tanks reached the enemy line, did they have any hope of stopping their opponent's assault?
With the British Mark series, grenades typically only worked for destroying them if utilized in the Geballte Ladung format, or 'concentrated charge'. This involved taking one stick grenade and wrapping 5-6 warheads from some other stick grenades around it, to increase the destructive power. This, however, could only be thrown short distances, and needed to land on top of the engine deck, so that the blast would be directed downwards into the engine.
This previous answer I've given may help:
That is the terror of the tank. It was hard for an infantryman to stop. Today there are all kinds of mines and anti-tank weapons but, even today if all you have is a rifle and some grenades a tank is a scary thing coming at you.