Mine? It's a mechanic shared by two "Naval" games, and it has a slightly different approach in each. Re rolling 6's for extra dmage effects.
In Full Thrust ( FT ), when firign beam batteries, the rolls of 6 do an initial two points of damage to the target vessel, half on armour, half on internal structure if armour is present, or all on internal if armour is not. Subsequnet re-rolls do dmage to internal structure, and each 6 does two points of damge and calls fro another re-roll; It is said to simulate the times when the firing ship has a solid "lock-on" to the avoiding target ship, and holds the energy beam on target long enough for severe damage to be done; Often leading to a single hit crippling many systems aboard the target vessel.
In Dystopian Wars ( DW ) the machanic is similar but is called Exploding Dice; Again, 6s are re-rolled and count for two points of hull damage. In one case, the "Devastating Munitions" feature of some guns, the first 6s rolled do two points of dameg and count for two rerolls in the next turn, and any 6s then count as a single re-roll from then on. Because of the way damage is done in DW, multiple two-point scores will build up on lucky re-rolls and lead to the immediate sinking of a vessel through a well-placed shot, whcih makes the Critical Hit mechanic truly critical tactically.
Both verisosn of the mechanic, I feel, give flavor to the game, allowing a fortunate hit to allow a small ship to deal to a larger one with fortunate shooting.
