The tube sock with Comp B in it.... Yeah it didn't work particularly well, mainly because most people blew themselves up with it (just like in Shaving Private Ryan)
Comp B is a mixture of TNT and RDX explosives, about 40/60 ratio respectively. Its a powerful explosive that is still used by some NATO suppliers to this day, but its not quite as handling friendly as C4 (Composition 4 or Composition C). It wasn't particularly effective because it lacked punch against armor, and when it was used effectively and never caused much damage except perhaps to the treads, which only made the crew angrier and want kill you more.
They were often used in conjunction with flanking attacks, were one (often suicidal) soldier ran up to the tank and placed it on the tread while the guys with Bazookas used the opportunity to sneak up behind a tank and then blow it up with a fine engine shot