Solver Rule: All ships (of one type) are found

There is one, and only one, way to place all remaining ships of a specific type.

Example

$images\fath0035.gif$

In the above board, there are two destroyers remaining to place. Examining the board, you can verify that there is one, and only one way to place the two destroyers:

ˇ (D,3)-(E,3)

ˇ (J,1)-(J,2)