Complex sentence: Upon going over the top Redmond, one of the first out of the trenches and leading his men, was hit almost immediately in the wrist and then, when hit in the leg, could do no more than urge his men on.
Split into simpler sentences: Upon going over the top, Redmond leading his men, was one of the first out of the trenches. He was hit almost immediately in the wrist and then, when hit in the leg, could do no more than urge his men on.