Crossing the T
Crossing the T is a tactic that dates back to the the earliest use of naval cannons. Sailing ships were long and relatively narrow to reduce total mass and reduce drag, so there was very little space to fit cannons in the bow of a ship of the line. The logical choice, therefore, was to place the majority of a ship's firepower in multiple decks along its sides (hence the term 'broadside').
"Crossing the T" refers to manuevering such a ship ahead of and roughly perpendicular to an enemy ship's path, allowing it to use it's full broadside firepower without exposing itself to much return fire from the target. While the target profile is harder to hit, the sheer volume of shots gives the ship "crossing the T" a greater chance of doing damage.
This tactic was effective (to varying degrees) up until World War II, when carrier-based aircraft largely replaced ship-mounted cannons as the primary means of attacking enemy shipping. The subsequent invention of long-range missiles and further advances in aircraft technology sealed this tactic's fate forever; it has not seen significant use for decades.
Crossing the T in Science Fiction
- In the Honor Harrington series of novels, crossing the T is an effective tactic due to the geometry of Honorverse Sidewalls.