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 used up until the end of World War II, where the use of long range aircraft that could attack without exposing their carrier to harm (indeed, they needn't even be in sight of the enemy) made this tactic less useful. 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.