Esna's been involved in a few fights, some involved in private, 'relatively' pre-planned storylines and some more spontaneous. Some have gone well, others less so. Unfortunately, I've also run across the "let me set my infinite super-soldier guard swarm on you" kind of thing, as well as the (for lack of a better way to put it) 'godmod-fighter' situation - i.e., "I run across the room and start beating you bloody..." On the other hand, I've also had some VERY good experiences with combat RP - both private with a single other RPer involved in a storyline with Esna, and in more "public" venues.
Personally, I view Esna as initially the product of the Imperial Navy training facility he went to. As such, he was competent with a sidearm and has knowledge (but not experience) of use of other small arms - but nothing more; not an especially good shot, not very good at hand-to-hand, and frankly inferior to the average ground-soldier grunt.
What I DO think fits with Esna's view of and experience with ground combat is that he learns from every single engagement. When he succeeds, he examines what tools helped him succeed; when he fails, he looks at the reasons for his failure and attempts to patch them over. At times I worry this has resulted in as much an "unbeatable" character as someone who was "overpowered" from the start, as Esna prefers to walk into a situation with every conceivable angle already covered, and most characters (and players) I end up fighting aren't actually prepared for a character who has thought through and prepared for the common options.
In the event Esna does have to get into a larger-scale fight, though, he prefers to rely on gadgetry and technology to cover his back - he'll at times deploy in a superheavy combat armor* that is equal parts light tank and command-and-control center, albeit hideously slow and probably noticeable from miles away.
It's important to note, though, that this isn't so he can pull a "space marine" charge straight into enemy fire - it's meant to enhance his skills (command, tactician) and cover his weaknesses (physically weak, not well skilled at combat) merely so that he can survive a potential ambush or unexpected contact with enemy. His preferred method is literally to spray out with the built-in weapons while calling for backup.
* This suit was conceived before DUST was even a thing. I have considered updating to one of the DUST suits, but decided that the dozen or so suits in DUST do not represent every model of suit available and that Esna could find something more suited to his needs.