This is a good start. My major issue with this is that you're not distinguishing your colors enough when you shaded the uniform. At a glance it looks like it's just one color, which is not what you want if you're trying to add detail to your sprites. If you can fix that then this is passable sprite work. All your shapes are readable and it's fairly clear what all these objects are (except for the thing on the rifleman's chest, it looks like a metal plate or something but I think it's supposed to be webbing?).
As for animation: At these sizes you have to exaggerate movements in order to communicate dynamic action to the viewer. People coil up, they lean back and bend their legs and torso, when they throw things in order to put more energy into it. Try experimenting with that a little. In a four frame grenade throwing animation I would have:
Frame 1: Getting ready, grenade held in both hands near chest to show he's prepping it to throw
Frame 2: Starting to throw, he leans back, back leg bends, front arm goes out in front of his body, throwing arm is extending
Frame 3: About to throw, he is fully leaned back, he is actually a pixel or two shorter because he is bent over, his throwing and off arms are fully extended
Frame 4: Post-throw, the grenade has left his hand, his right side has moved forward with his throwing arm
If you want to do a two-frame, just do frame 3 and 4.
Also, if that fireman is meant to be in direct combat and not a support role (as in rear echelon) I recommend you try a different design. Historically, combat flamethrower operators just wore the same clothes as everyone else, but I understand if you want flamethrower units to stand out.