Complex sentence: The "Wave"-class tankers are Royal Fleet Auxiliary "Fast Fleet Tankers" tasked with providing fuel, food, fresh water, ammunition and other supplies to Royal Navy vessels around the world.
Split into simpler sentences: The Wave "-class tankers are as class of fast fleet tankers" in service with the Royal Fleet Auxiliary. The class is tasked with providing fuel, food, fresh water, ammunition and other supplies to Royal Navy vessels around the world.