«How can you know where the shell lands, if you fire from behind a building?» asked Sela. «Does someone stand up on top of the building and tell the mortar people?»

Blade grinned. «You've got it exactly right. Each mortar needs not only a crew, but what we call in England a 'forward observer.' We will have to train these, as well as build the mortars. So it's time we got started.»

The industrial computers could turn any set of specifications into workable designs and then program the machine tools in the factories to build it. The problem was the shortage of competent computer programmers, reliable computers, and well-maintained machinery. Blade knew he would not be exactly popular in Mak'loh if the first mortar blew up and took its crew with it, so he insisted on taking everything slowly and carefully.

It was two weeks before the first mortar and shell were ready for testing. The mortar was a heavy, monstrously ugly thing that looked as if it had been made in a boiler factory and needed four strong men to carry it. Any Home Dimension army would have taken one look at it and fired the inventor rather than the mortar.

Its only virtue was that it worked. Blade demonstrated this, firing the mortar by pulling on a long cord from the shelter of a wall of sandbags. The shell flew more than two miles and landed with a puff of dust-a dud. The second shell flew just as far and went off with a tremendous explosion that threw a cloud of dirt and smoke a hundred feet into the air.

«That will probably go right through the roof of any building in Mak'loh,» said Blade, after examining the hole in the ground. «If you land one in the middle of a group of androids-«

«Please,» said Geetro, wincing at the image, «I can imagine well enough. Do we really need to produce these-monstrosities?»

«Yes,» said Sela and Blade, almost together. Blade let the woman go on. «We have to. Otherwise Paron will make them, as soon as he knows they are possible.» Blade was silent. He couldn't have put it better himself.

So the mortars and their ammunition went into production, and Blade started training the firing crews and observers. He set up the training range on the far side of the city from Paron's camp and had it heavily patrolled by armed androids. Military security was another thing he was having to reinvent.

Before too long there were five mortars, more than a hundred shells for each one, and a slowly increasing number of trained people. Blade picked out five buildings near the power station and on top of each one put a mortar, its ammunition, and its crew.

Normally everything was kept out of sight, well down inside the spiral ramp from the roof. When Blade gave the signal, the mortar crews would pick up their weapons and shells, rush up to the roof, and be ready to open fire in a minute or two. Blade carefully picked and measured aiming points all around the power plant, to save time in getting the mortars onto their targets.

As Blade said:

«Even if the mortars don't do that much damage, they will certainly be a surprise for Paron. I don't think he's prepared to face one, and that will be half the battle for us.»

It was nearly midnight, and everyone in the command post on top of the power plant was asleep except Blade. He himself was leaning back in a folding chair, his feet propped on top of the radio. It had been a long day, starting with seeing two new mortars come out of the factory and go off to the testing range. It was time to call an end to the day and get some sleep.

Blade swung his feet off the radio and stood up. As he stood, the silence of the night suddenly fell apart. Blade recognized the crackle of shock rifles and the crash of grenades. The noise seemed to be coming from the north-toward the area held by Paron.

«Up and alert!» Blade shouted. The people assigned to the command post jerked themselves awake and lurched to their feet. Blade pushed them aside and dashed out onto the roof. He ran to the edge, raised his binoculars, and looked north.

Along half a dozen streets solid masses of moving figures were flowing south. Distance made them ant-like, but the binoculars clearly revealed the red coveralls of soldier androids. A few black dots-humans in Authority coveralls-moved along the fringes of the red masses.

Ahead of them, each street was vanishing under a blanket of silver-gray smoke. As Blade watched, he saw the flash of grenade throwers, and the smoke clouds grew thicker. The front rank of androids seemed to move behind a fringe of white flame, as they fried their rifles continuously into the smoke.

Not a bad plan, thought Blade. Fill the grenades with some sort of chemical compound and use them to lay down a smoke screen. Then blast the area with rifle fire. He doubted Paron could have retrained the androids to kill a clearly visible Master in this short time. He might very well have managed to train them to fire blindly into smoke that might hide a Master. That way they could kill a hundred Masters without having to see one of them die or knowing for certain that they'd killed one. That would certainly make the androids a great deal more dangerous during one decisive battle, without making them permanently dangerous.

It also made any effort by Geetro's army to meet the attack in the open streets much too dangerous. Fortunately, they would not have to do anything of the kind-at least not until the mortars had done their work. If they did it.

A woman was bringing the radio out to Blade. He picked it up, switched it on, and punched the General Comman frequency.

«This is Blade. General alert, all hands. Condition Red, Condition Red. Paron is launching a mass android attack from the north. All human and android foot troops, remain in your buildings. Repeat, remain in your buildings. All doors should be locked and, if possible, barricaded with furniture.

«Mortar crews, prepare to fire on my command. Good luck, everybody.»

Blade picked up his binoculars again. By now the head of each column was vanishing under its smoke screen. The smoke screens themselves were creeping toward Blade down each street.

There was a planned aiming point for the mortars in each of the six streets. There was another in the middle of the square into which all six streets ran. When the mortars opened up ….

Blade waited until the head of each column was well past the aiming point in each street. The mortar shells ought to be scattered up and down the column for a considerable distance. Then he picked up the radio.

«Mortar teams-load and sound off.»

«Team One, loaded and ready!»

«Team Two, all ready!»

Then when all five had called in, Blade took a deep breath.

«All teams-Point 19. Fire on my signal. Five, four, three, two, one, FIRE!»

Five distant thumps came almost together, and then a long silence-mortar shells climb high and quietly. Then suddenly the street farthest to Blade's left spewed flame and smoke. Five shells plunged out of the sky, straight into the column of androids.

Blade did not hear the human and android screams and cries. He could imagine them well enough, for he knew what this kind of heavy fire did to infantry. Not just infantry, but infantry who'd never been trained to meet this kind of attack. None of them knew about mortar fire, and the explosions, the flying fragments, the smoke and the noise would be a nightmarish surprise to both humans and androids.

«Blade to all mortars. Shift to Point 17.» That would bring the shells down on the next column toward the right.

This time four shells were on target, while one plunged through the roof of a building on one side of the street. Even that shell wasn't completely wasted. Blade saw chunks of metal and stone from the roof hurled down on the androids below.

Four more times Blade shifted the fire of the mortars, moving steadily from left to right, hitting each of the six attacking columns in succession. Blade knew that it would be wise to shock and disorganize all six columns rather than wipe out one and leave the other five intact and advancing. Blade guessed Paron's androids outnumbered those of Geetro's army by three or four to one, apart from their new tactics with the smoke screens. Paron could not be allowed to get to close quarters, where those numbers might give him a decisive advantage.