Question:
Rule 20F3 clearly says transports may air transport, but not lay mines. Rule 23C (3rd bullet) says a transport may fly extended range minelaying missions. Which is correct? (Laying mines is a transport mission which only B and HB types can perform, but so why not say ” a bomber may fly extended range minelaying missions”?)

Answer:

In essence, a B or HB laying mines is acting as a transport and thus 23C is technically correct, but I see your point. Note also that the second bullet of 23C covers this situation implicitly, since aerial minelaying is one of “most bombing missions”, in that it is not explicitly stated as a mission wherein air units may not fly extended range, in the specific mission rules. Since the rules do not disallow extended range aerial minelaying missions, it follows that the rules do allow them.

Note also that transports may carry mines at extended range, as a transport mission, so the third bullet of 23C is correct as well.

Source:
TEM 53