The unusual spate of collisions, two of them fatal, has called into question the US Navy’s level of preparedness, analysts say, and point to potential problems with training, maintenance, or sailors’ workload. WASHINGTON—A recent spate of collisions involving US Navy ships from the Seventh Fleet, two of them fatal, has led the Navy to relieve that fleet’s commander, Vice Adm. Joseph Aucoin, reportedly after his superiors lost confidence in his leadership. The latest collision, Monday off the coast of Singapore, was between the guided-missile destroyer USS John S. McCain and a Liberian-flagged tanker. Ten sailors were reported missing, and the...