Ok so a few things!
1. I like where you’re going with the other Marines! I think right now I’m especially interested by Steven. I’m assuming he’s the “cold blooded killer” guy? I’m interested to know more of his background. I wonder what caused him to adopt this mindset! Has he been fighting for longer than the others, and maybe has become jaded and hardened by battle? Maybe he witnessed some truly horrific crimes caused by the insurgents, and ceases to see their humanity. Has he bought into propaganda or a sort of mob mentality that paints the enemy as somehow less than human? One thing that I’m curious about is if this causes issues within the squad. Jackson strikes me as a much more caring and compassionate person, and he seems to be more cautious when it comes to risk taking (like when he’s talking with Miles and expressing his doubts that he’ll survive.) Do you think that this might cause some tension? I’m really interested in his decision to sacrifice himself too. To me, it seems like he doesn’t seem to take death very seriously, or maybe doesn’t value life in general (even his own), which makes me wonder what his religious views are, or lack thereof. Also, this attitude towards life/death might cause him to push for riskier tactics!
I think Steven is interesting to me because he’s very clearly in the wrong sometimes. I think I personally tend to be drawn to messy characters, and I find them really fun to write. So for example, Kit (from the character castle) is probably my favorite character from my own project. I like writing Kit because he’s frankly kind of messed up and honestly REALLY annoying, but he’s trying so hard to get it right. I just can’t help but sympathize with him! And I’ve noticed that a lot in other media – the most fun and interesting characters are often the ones with very obvious flaws. So keep developing Steven, and consider what other flaws the rest of the marines have!
On that note, I think right now I have a hard time relating to Jackson because he seems like the perfect/ideal soldier. He’s compassionate, smart, and very competent, but he feels a little bit unrealistic because as far as I can see, he never falters.
I think you should consider letting him make a few mistakes every once in a while! That would not only make him feel more “real,” but also add emotional stakes, since any mistakes he makes could cause him to start losing his squads respect (it could be kind of interesting if he’s kind of “competing” in this sense – another person might have ideas that sound really appealing, but that Jackson knows could be disastrous in the long run.) Also consider, people tend to be less rational under high stress, so that could also cause some issues!
2. What’s the time period and location of this story? I’m assuming this is somewhere in the Middle East – are they fighting a terrorist organization? If so, I think it would be really helpful to nail a specific time and location, and start researching it. For example, researching the culture of the specific country would be really helpful, researching naming conventions in the country, etc.
3. One thing I’m a little bit confused about is how his squad is able to take out so many insurgents. Now, tbf I’m not very knowledgeable about military tactics and fighting, so you know a lot more than I do XD However, just from the perspective of an average reader, this sounds a little bit unrealistic. It makes me not fear the insurgents as much, because they seem to be easily killed and therefore not as much of a threat (which makes me not as emotionally engaged when the squad starts dying off). Also, when you have that much killing going on with low stakes, they can start to feel more like faceless robots than other humans that these characters have to kill.
One suggestion I have would be to gradually raise the stakes as the plot progresses. As the story progresses, have the fights get harder, the characters more desperate, and the deaths more shocking (I don’t mean pure shock value, but more of a deep emotional impact.) Maybe as the insurgents get desperate, they start sending out young, inexperienced, scared fighters. Steven might not have an issue with killing them, but I think it might weigh heavily on Jackson. Maybe the fighting puts some rescued prisoners in danger, or maybe some of the prisoners are locals, whose families could be harmed by the insurgents if they dare aid their rescuers. Start ramping up the stress too, so even if the insurgents aren’t getting stronger, the characters minds are getting more fragile. I think things like this will make your story more gripping and exciting as it progresses!
Anyways, this was a very long response and maybe a little bit of a ramble. This is just my two cents! Hope this is a good start 🙂
*laughs as one fey*