If the tanks on patrol (for example, in Market Garden or Neptune) seem like they are after you and you cannot get a decent shooting position, aim for their caterpillar tracks. This works best with a recoilless rifle or a Panzerschreck, but Gammon grenades will also work. With either of the rocket launchers, aim directly at the gears of the tracks and put a round through it. The tank will stop, making it easier to get ammo and take it out. With the Gammon grenades, throwing it directly up against the tracks or cook it so it bursts on contact or in the air next to it.