special attention was devoted to explaining the behaviour of the fixed weapon that had made the unauthorised strike against the incomer - the gun with the military codename E1. E1 had been totally destroyed by a series of powerful explosions and scarcely anything bigger than a micron was left of it. Furthermore, most of the material of which it had consisted, mixed with surface ice and water from Europa's ice-covered ocean, had either been scattered all over the Solar System or had fallen on Jupiter. This made things much harder for the military specialists trying to find out the reason for the unauthorised strike.

  All the logs of the weapon's technical parameters and of the communications between its gun crew, the command group and other ships were taken and subjected to intensive analysis. After finishing the investigation and putting together a picture of what had happened from minute fragments, the military did somehow manage to dig up one or two things.

  As we know, the space intruder had been told in the form of an ultimatum to take the dialogue to the political level. When it continued to evade specific answers, the group of military negotiators demanded that it leave the Solar System and withdraw beyond the heliosphere. The incomer had asked for 30 hours to consider this demand, on the grounds that it was obliged to have its actions approved by its superior command structures. With only a few hours left before the ultimatum expired, E1 had somehow become cocked and ready to fire.

  The system of subordination within the strike group was such that the command was unable to take complete control of the weapon remotely. The command could only take a weapon off safety and issue a command to the gun crew on site, but firing a shot or preventing one could only be done through physical access to the weapons.

  Without any information on the capabilities of the alien civilisation, the military did not want to risk activating remote access to their weapons. After all, the incomer might break through the protective perimeter and seize control of the space fleet. It was this shortcoming in the system that played a dirty trick on the fleet command. When E1 stopped subordinating itself to Rohas, he had no other way of putting it out of action except by destroying it.

  General Rohas had unsuccessfully tried to make contact with the gun crew. At that precise moment, the alien ship was outside E1's zone of visibility. Rohas then ordered the ships of the second echelon, attack ships intended to prevent strike weapons from this very sort of independent activity, to fire a warning shot.

  There had been no reaction. Unfortunately, it would never be possible to find out whether the gun crew had lost its nerve at that moment, or if sabotage had taken place, or if they had gone out of their minds or were even dead. Since the incomer was quickly entering E1's strike zone, the decision was taken to neutralise the combat-ready gun together with its crew.

  The second echelon command ship fired, but missed. It tried again and again, each time without success. It then fired a volley from every weapon under its command. Ten powerful ships let loose a storm of fire on Europa to compensate for any excessive targeting error.

  As a result of the explosion, the satellite lost about one per cent of its mass. A huge quantity of ice, dust and rock was ejected into space, the temperature of Europa's ocean rose by several degrees over an area of several thousand square kilometres, and the celestial body changed its angle of rotation around its own axis and its orbit around Jupiter.

  Nevertheless, E1 had had time to fire at the alien ship. The delay due to the targeting error of the second echelon command ship turned out to be enough for the shot to be fired.

  The incomer, caught at a tangent by the explosion, had been ejected from its former orbit, after which it rapidly accelerated and disappeared into the depths of space.

  The command was concerned with three questions, on which the investigation concentrated. Why had the random cocking of the weapon taken place? What had happened to the crew, since there had been no reaction either to attempts to contact it or to the warning shots? And why had the attack ships of the second echelon not been able to put E1 out of action with the first shot?

  When it is a matter of military operations on Earth, there always remains the possibility of concealed agents, 'sleepers', who can undertake a sabotage operation on the enemy's instructions. But the idea that Earthlings could be recruited by the aliens seemed absurd, and was not considered credible.

  They did not succeed in finding a sensible explanation for the behaviour of the crew of E1 in the minutes before it fired. There was constant monitoring of the atmosphere in their living accommodation, so poisoning by some kind of gas, or loss of seal, could be discounted. The motion sensors did not register any foreign objects. No non-standard activity was recorded. The behaviour of E1's gun crew directly before it was destroyed remained a mystery. The only thing that was known for certain was that the order to take the weapon off safety must have been given from within. E1 did not receive any order remotely.

  There is rarely one single reason for a catastrophe of technical origin. More often than not, a whole chain of circumstances lies behind it, and what happened to E1 was no exception.

  The situation in which E1 escaped from the command's control had been considered possible, so in this case, the strike group blockading the alien ship had included the second-echelon ships. The second echelon had the specific task of destroying weapons not responding to orders, as a last resort. Unfortunately, however, even these safety measures had proved insufficient.

  When it became clear that control over E1 had been lost and it would be impossible to restore it within an acceptable time, a shot was fired at it by one of the second-echelon ships. The anti-matter charge missed the target and struck the surface of Europa hundreds of metres from the targeted point. Since the charge had been fired from a distance of only a few tens of thousands of kilometres, a distance from which a miss was not expected, its energy had not had an excess reserve. But it would have been enough to put E1 out of action and possibly to save the lives of its crew.

  As was discovered later, the reason the charge deviated from its trajectory was an anomaly that had been discovered a few days earlier by Professor Shelby's team. At the time of the events surrounding E1, the existence of this anomaly was already known to the Space Fleet High Command. Unfortunately, the facts known about it at that time and the brief time interval had not been enough to work out an effective strategy for counteracting it. The situation was complicated by the fact that the greater the energy of the anti-matter charge, the more the anomaly distorted the trajectory of the space weapon. Not having come across such a phenomenon before, the aiming computer was unable to recognise the distorting factors. The only solution programmed into it was to use excess strike energy.

  Using enough force to produce a huge crater in the surface of Europa, E1 was finally destroyed. But by turning the disobedient weapon into fine dust, the second echelon had buried forever the last hope of fully explaining the reasons for the control failure. The Space Fleet High Command had no option but to be content with theories.

  The first of these assumed a technical failure of E1's built-in computer. Obviously, any such failure would have to have affected not only the targeting module but also the communications module, which had made it impossible to establish contact with the command ship. The gun crew might have been trying to restore control, and for that reason did not react to the warning shots, knowing that restoring control was the only thing that could save them from being destroyed. There was simply not enough time to contact the command ship by any other means.

  Another theory assumed that E1 had been acted on from outside. Looked on as a false flag operation, loss of control over it followed by a strike at the alien ship made sense, but raised a series of problems of a technical nature.

  To break through the defences of E1's computer would require profound knowledge of its internal structure. Such information could be acquired by re-engineering after infiltrating the weapon system on site or while it was being transported to its place of deployment.

  Since mankind
had long since mastered the technology of manufacturing and using nano-robots, E1, like any other modern weapon, had the means to protect and counteract the penetration of nano-machines into it, protecting not only its internal electronics, but also living personnel.

  For successful and imperceptible penetration, the means of infiltration would have to be smaller than nano-objects, yet possess considerable computing power. The creation of such robots came up not against technical difficulties, but a theoretical threshold. Such unimaginably small devices could not possess such unimaginably great computing power. In this case, the re-engineering and subsequent control of the weapon would require an incredibly impressive computing apparatus.

  There also remained the possibility of infiltration at the production stage. This theory also had many weak points. For example, how would the incomer know precisely what weapon would be used in the blockade? It was logical to assume that it could not know this, and therefore would have needed to infiltrate numerous arms factories. If they had, it would mean that most of Earth's military production capacity was compromised. Furthermore, if the alien civilisation had such means of infiltration at their disposal, what was