There was some danger to the operator in handling a highly inflammable oil. The blaze might flare back and burn him, particularly when he was lighting the stream, and so a special way of setting fire to the spray had to be devised. Of course, the value of the apparatus lay in its power to shoot the stream as far as possible. The compressed air would send the stream to a good distance, but after lighting, the oil might be consumed before it reached the desired range. Some way had to be found of igniting the oil stream far from the nozzle or as near the limit of its range as possible. And so two nozzles were used, one with a small opening so that it would send out a fine jet of long range, while the main stream of oil issued from the second nozzle. The first nozzle was movable with respect to the second and the two streams could be regulated to come together at any desired distance from the operator within the range of the apparatus. The fine stream was ignited and carried the flame out to the main stream, setting fire to it near the limit of its range. In this way a flare-back was avoided and the oil blazed where the flame was needed. The same sort of double nozzle was used on the stationary apparatus and because weight was not a consideration, heavier apparatus was used which shot the stream to a greater distance. But flame-throwing apparatus had its drawbacks: there was always the danger that the tank of highly inflammable oil might be burst open by a shell or hand-grenade and its contents set on fire. The fixed apparatus was buried under bags of sand, but the man who carried flame-throwing apparatus on his back had to take his chances, not knowing at what instant the oil he carried might be set ablaze, turning him into a living, writhing, human torch. Because of this hazard, liquid fire did not play a very important part in trench warfare; to set fire to the spray at its source with a well directed hand-grenade was too easy. THE "FIRE BROOM" There were certain situations, however, in which liquid fire played a very important part. After a line of trenches had been captured it was difficult to clear out the enemy who lurked in dugouts and underground passages. They would not surrender, and from their hidden recesses they could pour out a deadly machine-gun fire. The only way of dislodging them was to use the "fire broom." In other words, a stream of liquid fire was poured into the dugout, burning out the men trapped in it. If there were a second exit, they would come tumbling out in a hurry. If not, they would be burned to death. After the first sweep of the "broom," if there were any survivors, there would not be any fight left in them, and they would be quick to surrender before being subjected to a second dose of fire. CHAPTER VI TANKS