The first story, "Run Rabbit, Run!" is classic Sam Glanzman. The second screams Bill Molno, and, sure enough, GCD credits it to Molno, with Sal Trapani on inks. I'll have to disagree. These faces are Molno-Mastroserio:
The next story, "Assault Team!" gets no GCD credit, but I feel confident giving it to Molno, with Vince Alascia on inks. Notice, in particular, the Bill-Vince faces in the splash panel:
These next two panels, from the story's second and last page, clinch it for me: The first shows a classic Bill-Vince depiction of jagged steel (Bill and Vince's torpedo-damaged hulls look about the same), and the second features standard Molno-Alascia background figures.
The looser Bill-Vince inks of the early 1960s had yet to arrive.
The last tale, "The Unseen!" (note the ! in all of this issue's titles) is the most interesting, art-wise, because of the combination--namely, Bill on pencils, and Tony Tallarico on inks. Yes, Tony Tallarico. (UPDATE: After studying more examples, I'm leaning toward Vince Colletta.) Check the faces:
And notice the Molno-style explosion (simple and efficient, with a minimum of background detail), followed by the Molno-style insert panel:
"Rat-Ta-Tat!"? Imagine being mown down by a lousy "Rat-Ta-Tat!" Or maybe that's all the writer and/or artists thought the enemy deserved? This is Fightin' Marines, after all. I suppose it's better than perishing with a "Voooosh!" (I'll have to verify that spelling.)
Again, I'd rate myself 80 percent sure on the Molno-Tallarico credit. At the very least, we're seeing Molno layouts, which is very possible, given the period. By the way, I'm basing my Tallarico i.d. in part on the following 1959 issue of Space Adventures: Comic Books Plus. Note the artwork of the two stories ("The Long Wait" & "Captive from Space") tentatively credited to Tallarico. That's our man. (The same artist also drew "Prison Ship in Space" in the No. 24, Oct., 1960 issue of Unusual Tales.)
UPDATE TO THE UPDATE BELOW: Vince Colletta seems like a better candidate for the inks in "The Unseen!" Here's a page (borrowed from The Charlton Comics Reading Library) from Space Adventures, No. 33 (March, 1960) featuring Molno-Colletta art. It doesn't precisely match the Fightin' Marines art, but then we're talking nearly a year's difference, plus a different genre. So, maybe:
Compare it to these faces from "The Unseen!":
UPDATE: Here's our mystery artist, be he Tony Tallarico or someone else (Vince Colletta?), in Battlefield Action, No. 17 (Dec., 1957). No credit(s) at GCD. Scanned from my copy:
The final story of the issue, Teddy Roosevelt and His Rough Riders, is also without a GCD credit, but it's majorly Molno (on pencils and inks).