The Titan Incident was a confrontation between the United Federation of Planets and Romulan Star Empire that occurred in 2294.
The USS Titan (NCC-2014) exploded shortly after the USS Valkyrie (NCC-2590) had transported the Federation President and his assistant over to the ship. The Valkyrie's crew successfully unravelled a Romulan plot to fake the destruction of the Titan, in order to steal its technology. The Valkyrie was later forced to enter the Neutral Zone in pursuit of a cloaked ship, violating the Treaty between the two powers. (Star Trek: Valkyrie: "A Problem of Titan Proportions")
At the time, Romulan propulsion systems were known to be less advanced than those of the Federation and had been for some decades. (TOS: "Balance of Terror")
The event was memorable enough to be told as a tale for several other Starfleet captains when Edward Stanfield visited The Captain's Table. (Star Trek: Valkyrie: "The Captain's Table")