Sky Menace (SM) has default 3+1 transport capacity; if you buy "Air Transport Capacity I" upgrade you get capacity 5; with the second upgrade you get up to 6 capacity.
Remember, SM is a high-cost strat (needs high-income countries and space for expansion; it is slow expansion in games below 15k) with great mobility and very strong bombers. You can move bombers to attack/defend between cities far apart.
A list of upgrades yu can find
HERE.