Complex sentence: For this attack, Wilder-Neligan had split his command into two specially trained "storm" companies, with his other two companies responsible for carrying forward ammunition and equipment and for "mopping-up" of pockets of resistance.
Split into simpler sentences: For this attack, Wilder-Neligan had split his command into two. The assault would be carried out by two specially trained "storm" companies, with his other two companies responsible for carrying forward ammunition and equipment and "mopping-up" of pockets of resistance.