Complex sentence: The ships of the Omaha class spent most of the time deployed to secondary theaters and in less vital tasks than more recent cruisers, in places where their significant armament might be useful if called upon but their age and limited abilities were less likely to be tested.
Split into simpler sentences: The ships of the Omaha class spent most of the time deployed to secondary theaters and in less vital tasks than those assigned to more recent cruisers. The Omahas were sent in places where their significant armament might be useful if called upon, but where their age and limited abilities were less likely to be tested.