Think about it: Eve is sent down to Earth to search for plant life. So why give her an arm cannon? What need or use could it possibly have for it?
If they were sending it to some completely alien, unexplored world where they didn't know what it might encounter, then an arm cannon would make perfect sense. Here though, I can't figure out what the point of it was. Isn't this kind of like giving an archeologist an uzi just before he goes to dig for dinosaur bones?
Who says it was ment as a cannon and not the advanced version of wall-e's lazer cutter? I mean if you were building a probe and you decided to give it a cutter would you not give it the most powerful one possible so it could cut through thicker things faster? A single pulse from a realy powerful lazer would seem like a cannon blast because of the rapidly vaporizng material expanding, if it was fired at a higher threshold than neccessary. Also there is the fact that the movie is placed 700 years after people left earth, there is no gaurentee that they all left and that when the probes returned after the orginal 5 years they would not have to deal with savages or mutants. There is also the fact that an explosion of any kind, so long as you can withstand it undamaged, can be useful in escaping if you were say burried under an avalanch of some kind (or in a giant block of garbage like eve was whn she blasted herself out).
If you wonder what God thinks of money look at who he gives it to
I know this really looking deep into it but the fact that the escape pod ejected flares (a countermeasure used to deflect heat seeking missiles) would imply that the axiom was designed with the possibility of an armed conflict in mind. She could have been armed to protect the axiom in case the need ever rose.
She may have been like a modern predator drone. A recon device with a limited combat capability.
Another one is it assisted space mining. Or she was designed with multiple uses in mind.
What I thought strange was the huge number of "Eve" type robots which I guess are deployed all over the earth, and yet the big carrier ship descends from space, drops just one robot off, then flies back up to space again. How inefficient is that?