First up, a correction. The British Expeditionary force starts the game concentrated at Aswan. Every move I can roll a D6 and release that number of units for operations starting either there or at Suakin.
I rolled a 5 and will therefore have five units transported by the sea route to Suakin. These will be three infantry, one cavalry and one gun.
To determine what happens when they debark, I need to roll more than the regions' revolt index for the Dervishes NOT to meet me in the field. As the RI for the Western Sudan is 6, there is no chance of this happening, therefore we will fight.
To determine the composition of the Mahdist force one deducts the die roll from the RI. As I had rolled a 5, the enemy has one unit to oppose me. Two, since Suakin is a Garrison Town worth five points. I then roll again for each unit to determine the type: I roll two fours. On a 4-6 one gets Ansar. Thus my British force of five units will face a Mahdist force of two Ansar units.
Now, on the balance of probabilities, I would think the Ansar would get rolled over pretty quickly and that they would not in fact actually offer battle. Therefore I am going to consider that the BEF enters Suakin unopposed.
More updates as I work through.