If I have two thieves on an attacking sub what happens?

A) Only one has any effect: 15% of enemy's drillers converte to my side.
B) Both have effect in a combined: 30% of enemy's drillers convert
C) Both have effect in a sequential fashion: 15% of enemy's drillers convert followed by another 15% of the remaining drillers convert (in other words, 27.75% of the original total convert. 15% + 15% x 85%.)

Which of the above would take place?
Thanks.

the correct outcome should be B. if you see otherwise, let me know.

Very good. Thanks Ron.