US Navy destroyers and cruisers needing to leave the ongoing battle against Iran-backed Houthi rebels with missile and drone barrages in the Red Sea, to reload their Mk 41 Vertical Launching System (VLS) missile cells are causing a presence gap and "a real challenge," Navy Secretary Carlos Del Toro said Wednesday at the annual Surface Navy Association conference. That challenge extends not only to the Red Sea campaign, he said, but especially to a future war with China across the vast West Pacific expanse as well.