I've seen them firing many times, but I've to confess that I've never seen one of these missiles systems getting loaded. It seems as easy as inserting a cartridge in a Nintendo Entertainment system.
ATLANTIC OCEAN (May 20, 2014) Sailors assigned to the combat systems department of the aircraft carrier USS Theodore Roosevelt (CVN 71) prepare to load an Evolved Sea Sparrow missile system [ESSM]. Theodore Roosevelt is underway preparing for future deployments.(U.S. Navy photo by Mass Communication Specialist Seaman Apprentice Wyatt L. Anthony/Released) 140520-N-VH385-010
The ESSM is a missile designed to destroy supersonic anti-ship missiles, so they are crucial for aircraft carriers and any other ship. Here's a video of it being fired: