This PIAT (below) knocked out a Tiger with its first shot, sure it was only a partial pen but it did the job.. :)
In another game a Tiger was ambushed by several PIATS which peppered it with 6 hits, all of which were partials but the monster refused to die, then a 7th partial finally knocked it out.
The moral? - partials can kill any tank even if the firing weapon can't get a full penetration.
BTW, Because PIATS fire a round propelled by a cartridge they have no smoke backblast to give away their position, which is a great advantage over the smoky rocket-firing schreck and bazooka..
In fact PIATS don't go whoosh at all but have somehow gatecrashed this Whoosh thread..