When using a bomb, is the prerequisite the same as an attack when the dragon is surfaced and/or cave is collapsing? That is strength must be >= armor (roll if equal).
Edit: Retracted -- see below.
No. You can only use a bomb against the dragon when he is underground and the collapse has not yet started. The strength requirement is only applied when the dragon is surfaced. Therefore, your strength stat is irrelevant when using the bomb.