Police had been contacted by a member of the public who raised concerns about the man on Monday morning, who was believed to have left the shore in a small boat.
Brixham coastguard assisted with the early stages of the search while Devon and Cornwall Police continued the hunt for the man.
In turn, at around 10.50am the MoD Police supplied a RIB to assist and acting on information supplied by other boat users the rescuers congregated on a vessel at the western end of the breakwater.
A police spokesman said: “The man was found in the water, fully clothed.
“We had received information that the man may have had a weapon and as a result two officers had been dispatched with Tasers after being picked up from Royal William Yard, to support our MoD colleagues.
“The Taser authorisation was in case of any threat posed by the male to officers or to himself, once he was back on board a boat.
“The MoD police recovered the male back to his own boat and he was escorted, with a police officer on board his boat, back to the Mayflower marina.
“There, he was assessed by paramedics before being detained, under the Mental Health Act, by officers. He was then taken to Derriford Hospital for treatment.”