The ships at the top of the T (those 'crossing') have the advantage. This is because all the main guns of all of their ships (in the older days of sail, a full broadside) can engage the ships in the bottom of the T which are sailing directly into the guns in a line. The advantages are:

  • Broadside. As noted, all the guns of the crossing flotilla can bear on target (or all the guns of the relevant broadside) whereas the guns of the bottom of the T can't bear at all (or in the case of more modern turreted weapons, perhaps half of them can, and only a few ships have unrestricted views of the target).
  • Relative motion. The ships sailing towards the line, at the bottom ('targets' hereafter) have a target that is crossing left to right or right to left relative to their gunfire at a speed they do not control and must estimate. The firing flotilla has a target that is advancing directly towards its guns, ergo is stationary in the gunsights at the moment of firing.
  • Evasive maneuvers. Any evasive maneuvers by the target flotilla will increase the silhouette it presents to the enemy, whereas evasive maneuvers by the firing flotilla will decrease the silhouette it presents.