She visited Devonport dockyard and boarded the Royal Navy vessel which underwent a revamp of its weaponry, internal systems and living quarters.
She later attended a rededication service for HMS Ocean.
The Queen met Plymouth civic dignitaries at the city's railway station before travelling to the naval base.
Labour councillor Neil Hendy and local Conservative MP Oliver Colvile tweeted welcomes to her.
A 21-gun salute announced the Queen's arrival at Devonport before she boarded amphibious assault ship HMS Ocean.
HMS Ocean - the sixth vessel to carry the name - was launched in 1995 and commissioned into the Navy three years later.
After the 2012 London Olympics, in which the ship provided security on the Thames, it underwent a revamp at Devonport of its weaponry, internal systems and living quarters.
HMS Ocean's second-in-command Cdr Tony Rackham said: "This is the culmination of years of preparation of the ship from refit to getting ready for sea and operations and then rehearsing for our royal sponsor.
"It can't get any better than this. It's real reward for all our hard work.''
A Buckingham Palace spokesman said: "Every Royal Navy warship has a Lady Sponsor and Her Majesty The Queen holds this title with Ocean.
"The relationship continues throughout the life of the ship, each successive captain keeping Her Majesty informed of the ship's activities and hosting visits.
"The rededication ceremony marks the ship's return to operational service following completion of her refit and subsequent work up.
"It provides an appropriate occasion for Her Majesty The Queen to reaffirm publicly her link to HMS Ocean and meet the new crew."
The Queen has visited Plymouth to view the results of a £65m refit of HMS Ocean.