From Closing with the Enemy by Michael Doubler:

"On 16 September Montbarey's besiegers literally hammered, burned, and blasted the fortress into submission. The Churchill [flamethrower tanks] delivered the opening blows by circling the fortress while scorching it with plumes of flame. Montbarey's walls had proved impervious to direct and indirect fire, so the battalion commander decided to smash his way inside through the main gate. A TD [tank destroyer] rolled forward and fired fifty rounds at point-blank range in an attempt to open the entrance. However, the Germans had reinforced the gate with scrap metal, rocks, and heavy debris, and it refused to budge. The TD's unsuccessful efforts prompted the battalion commander to send for a 105-mm howitzer, and in a scene similar to the siege operations of eighteenth-century warfare, soldiers brought the gun forward and placed its muzzle twenty yards from the main gate. The cannon hammered the gate partially open with more than fifteen rounds and then sent numerous high explosive and white phosphorous shells slamming into the inner courtyard."

Wow. That would have been something to see, huh? Must have been a hell of a door.