Each carrier based aircraft, including jets (see the optional rule Research & Development) rolls 2 dice. Submarine including Super submarines (again, the optional rule) rolls 2 dice.
All surface warships, except an aircraft carrier, rolls 1 die.
All rolls of 3 or less are counted. This total is the number of IPCs the turn player will lose due to convoy disruption(s). Note: A disrupted convoy canít lose more IPCs than the total IPC value of controlled territories or islands adjacent to the sea zone, and each territory may not lose more than its IPC value to more than one disrupted convoy.
--this is from the rules for convoy disruptions-that means the sub would roll two dice
Rolls: 2@3; Total Hits: 0
2@3: (5, 4)