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Faced with such an unfavorable situation, although the four high-level demon lords were very angry in their hearts, they did not react, and they all chose to wait.

For them, it is not impossible to attack such a difficult bone quickly, and it is a question of how much it costs.

Ordinary cannon fodder troops obviously can't deal with Emperor Shitian's almost perfect defense, at most they are fighting for attrition, exchanging their huge casualties for a small number of casualties on the other side, which is obviously a great loss.

And if you want to make a breakthrough, then you must use elite troops, at least they are also composed of high-level troops above the level of pure silver, and as soon as they are dispatched, tens of millions will be gathered together, and then the legendary masters will escort them to help them resist long-range firepower, and at the same time, they must also deal with the opponent's legendary sneak attack.

If you do this, whether you can build the opposite line or not, your side will definitely suffer heavy losses.

Because in this chaotic battlefield, whoever can't hold his breath first and invests his elite troops will be tantamount to falling into a disadvantaged position and being in an absolutely passive position.

Because the duel between the elite and the elite often depends on the first move, whoever can launch a surprise attack on the opponent's elite first is almost equivalent to winning more than 8 percent.

Although the elite troops are powerful, if they are to be fiercely targeted by others, if they are fiercely attacked, they will definitely suffer heavy losses in an instant.

So generally speaking, in a large-scale war, a huge number of cannon fodder fights each other, and elite troops are hidden.

If anyone can't hold on to cannon fodder and is forced to use elite troops, it is equivalent to exposing their elite troops to other people's targets, and the probability of being attacked by others is very high.

This point of view is also suitable for those strong people above the level of legend, and the battle between them is often the first to strike, if anyone is sneak attacked, who is equivalent to completely falling into the disadvantage, and the chance of losing is very large.

Therefore, the legendary master does not dare to expose himself easily on the battlefield, so it is easy to be attacked by the opponent's legendary master.

For example, the legendary masters found by the assassination team this time, although they repelled the gold-level team that assassinated them, but after they were exposed, they would be immediately besieged by the legendary masters, and the end would often be very miserable.

Emperor Shi Tian is also the same on his side, if his legendary master dares to be exposed to the city wall for a long time, he will definitely be besieged and killed by the other party's legendary master.

Therefore, the legendary powerhouses on Emperor Shitian's side are also very well hidden, even if they make a move, it is only a flash in the pan, and they run away after the fight, and they don't dare to show up for a long time.

In this case, as long as the four high-level demon lords were not crazy, they would not be willing to expose their elite troops and legendary powerhouses.

So these cunning guys have chosen to wait, and would rather sacrifice some more cannon fodder to hide their elite.

In addition, it is worth mentioning that the four high-level demon lords are also very knowledgeable people, and they actually vaguely see an Achilles heel in Emperor Shitian's defense line at this time, that is, the sustained ability of the super heavy artillery.

You must know that the larger the caliber of heavy artillery, the higher the wear and tear on the gun chamber.

Emperor Shi Tian vaguely remembered that when he was in the Nether, after the caliber of this relatively primitive gunpowder weapon exceeded 1,000, the life of the cannon barrel was basically reduced to less than a few hundred.

This means that after shelling hundreds of shells in a row, the bubble tube can be scrapped.

Of course, Emperor Shi Tian has now entered the Magical Age, and although the barrels of these cannons are only at the intermediate alchemy level, their wear resistance far exceeds that of the Nether, at least they can support the cannons to continuously bombard tens of thousands of shells.

It's just that in this process, there needs to be a mage to constantly cool down the barrel, and an alchemist to take care of it, and from time to time to perform a restoration technique to make the worn barrel repair automatically.

It is precisely with these operations that can be called against the sky that the batch of super heavy artillery in Emperor Shi Tian's hand can still shell for several hours in a row, and his face does not change his color and heart does not beat, and he still fights very happily.

But the problem is that the loss of the barrel of the super heavy artillery is not infinite after all.

After the barrel of such a long and thick gun is worn, even if it is an ordinary restoration technique, there is no guarantee that it will be 100% restored to its original state.

Especially after the continuous release of the recovery number, the life of the barrel will also have a certain impact, and even gradually make the barrel soft.

Therefore, when a certain level is reached, the barrel must be replaced, and the replaced barrel needs to be treated with special alchemy, at least a few days of recuperation, and then it can be completely restored, and then it can be used in battle again.

Then the problem comes, the super heavy cannon is so huge, a barrel weighs hundreds of tons, if this thing wants to be replaced, hehe, it is not a simple matter, anyway, it will have to be tossed for two or three hours.

Of course, there is also a way not to toss, if you can dispatch a legendary-level alchemist, you can quickly care for it without disassembling the barrel, and then you can continue to attack non-stop.

But unfortunately, although the legendary alchemy mage Emperor Shi Tian had some, it was absolutely impossible to maintain hundreds of thousands of super heavy cannons in a short period of time.

So this means that there will be a big pause in the three firepower defense lines created by the super heavy artillery, and at that time, the demon army will be able to pour under the city wall like a tide, which will definitely cause terrifying damage, and maybe the city wall will be demolished by others.

Although the four high-level demon lords are not familiar with alchemy artillery, especially the super heavy cannon invented by Emperor Shi Tian, they have also lived for so long, and they are not too unfamiliar with alchemy, and they must know the secret that alchemy cannons cannot be fired indefinitely.

Therefore, the four high-level demon lords 8 Cheng judged that there would be a time for this batch of artillery to stop for maintenance, and that was the time for them to attack with all their might.

I have to say that these 4 treacherous and cunning high-level demon lords are indeed very calm, and Emperor Shitian's idea of abolishing the opponent's elite troops at the beginning can be declared frustrated.

Originally, Emperor Shi Tian felt that the four high-level demon lords must be murderous and conceited people, as long as they were beaten miserably at the beginning, these murderous, arrogant and conceited guys would be in a hurry to retaliate, and maybe they would send their elite troops out.

At that time, Emperor Shi Tian can use his hidden power to severely damage the opponent's elite troops, and kill a group of legendary masters on the other side.

As long as this strategic goal can be achieved, then even if Emperor Shi Tian loses the first line of defense, it will definitely be considered earned.

But it was obvious that Emperor Shi Tian underestimated the wisdom of these four high-level demon lords, they were not fooled, and would rather risk huge casualties than hide their elite troops, and not give Emperor Shi Tian a chance to sneak attack at all.

And in this way, Emperor Shi Tian is a little bit of a wax, who told his super heavy cannon that he can't fire infinitely?

Seeing that the other party was not fooled, Emperor Shi Tian had no choice but to reluctantly order the use of a backup plan.

In fact, the so-called backup plan is to transport new super heavy artillery.

Emperor Shi Tian has such a huge industrial base, and so many alchemists, to make this kind of low-cost, low-tech weapon, it is simply not too simple, not only there are a lot of super heavy artillery on the back of the defense line, but even his warehouse is constantly piling up the super heavy artillery that has just been produced.

In short, with Emperor Shitian's order, the logistics department that had been prepared immediately started.

After the light of teleportation flashed, the strongest transport unit, the Void Dragon, teleported all the super heavy cannons stored in its body to the pre-designated location.

These positions are next to the firing super-heavy artillery, where there is a reserved open space for them.

After the super heavy cannon is teleported, those troops who are firing the cannon will immediately use a group of reserve gunners to come and place the super heavy artillery.

The super heavy artillery that had just been sent over was still in a state of transportation, and there was no way to fire it directly, so those reserve gunners came over to regulate it.

First of all, the intermediate mage took action, using the levitation technique, to float the entire super heavy cannon up, and then those giant gunners began to put down the bracket of the heavy cannon, and then put some other bits and pieces in place.

It took a full 10 minutes for the super heavy cannon to enter the firing state, and then it was slowly lowered to the ground.

At this time, the giants began to fix the cannon mount, and the recoil of this thing was amazing, and if it was not fixed enough, it would not be able to fire continuously.

After another 10 minutes or so, with the help of the mage, the gun carriage was completely fixed on the ground with the spell of turning mud into stone, and the preparation for firing was completed.

Then the giant began to turn the pulley on the gun mount, slowly raising the muzzle of the gun for the final aiming work.

When it was all over, the new artillery was put into service, and at the same time, the heavy artillery, which had been shelling for several hours, stopped shelling.

After completing the alternation, the Giant gunners began to disassemble the already hot barrels.

Even if there is a spell that keeps cooling down, after several hours of continuous shelling, the temperature of the cannon barrel still rises a lot uncontrollably, and it is even a little hot.

Fortunately, the giants have rough skin and thick meat, so they don't have to care about this little flaw.

With the help of the mage, they had to work hard to remove the old barrel.

At this time, the new barrel was also teleported, and it was quickly installed.

As for the old barrel, it was teleported to the rear and began the alchemy repair work, which usually lasted several days before it could be repaired as before, and it also required the use of valuable repair liquid.

But in any case, each barrel consumes a lot of steel, even magic metal, and it is a pity to scrap it like this, and the cost of repairing it is much less than buying a new one, which is definitely a good deal.