Complex sentence: The bridge crew on "Melbourne" assumed that "Voyager" was zig-zagging to let the carrier pass and then assume position, while senior personnel on "Voyager" were not paying attention to the manoeuvre.
Split into simpler sentences: The bridge crew on "Melbourne" assumed that "Voyager" was zig-zagging to let the carrier overtake her, and would then assume her correct position. Senior personnel on "Voyager" were not paying attention to the manoeuvre.